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This paper presents a Large Eddy Simulation (LES) study investigating jet flame ignition characteristics to achieve stable ammonia combustion for novel applications in gaseous ammonia/hydrogen-fueled engines with an active prechamber. The study investigated three cases with initial global equivalence ratios of 0.6, 0.8, and 1.0. Two main ignition modes were proposed, and five stages of coupled flame propagation processes were identified. The oscillation of supersonic hydrogen jet flame was investigated. The modes of flame-vortex interaction including vortex ring formation, along with the mechanism of highly reactive zone formation, were proposed. The effects of reactivity and turbulence transition on piloted ammonia flame were investigated to attain stable ammonia combustion and achieve a high heat release rate. The results showed that oscillations in the jet flame were strengthened at low global equivalence ratios with high hydrogen mass ratios. Enhancing propagation of initial and secondary vortex rings broadened highly reactive zones. Vorticity dissipated more rapidly at low equivalence ratios, leading to a stratified structure and enhanced piloted spherical flame. The Unsteady Flamelet Ignition Prediction (UFIP) sub-model of combustion was verified for the piloted ammonia flame, enabling a more comprehensive discussion of flame propagation tendencies. • The transient characteristics of jet flames ignited by H 2 /NH 3 mixtures were analyzed using LES. • The behavior of stratified flames at various equivalence ratios was investigated. • Various modes of turbulent jet flame ignition were proposed according to different stages. • The mechanism of vortex evolution to form the reactive zone and pilot flame was proposed. [ABSTRACT FROM AUTHOR]

The direct combustion of by-product hydrogen is a promising way for reducing costs and greenhouse emissions. Coke oven gas (COG) which is mainly composed of H2, CH4 and CO is a major source of by-product hydrogen that is suitable to be adopted by internal combustion engines. This paper investigated the COG combustion in a spark-ignition engine with Miller cycle. To get an overview of by-product hydrogen combustion properties, two kinds of COG compositions with the maximum and minimum hydrogen fractions were tested. The excess air ratio (λ) was raised from stoichiometric to the lean limit to explore the capability of COG on improving the engine performance under a common-driving speed of 1500 rpm and part load conditions. The test results indicated that the engine fueled by COG with higher hydrogen fractions could gain concentrated heat release period, extended lean burn limit, reduced HC and CO2 emissions, and enhanced working capability only at ultra-lean conditions. The properly increased λ availed improving engine efficiency and lowering HC emissions. The peak indicated thermal efficiency of 38.6% was acquired at the λ of 1.2, while the lowest HC emissions of only 32 ppm was gained at the λ of 1.4. Under ultra lean conditions, NO emission dropped to near zero, and CO from the by-product hydrogen-fueled engine was negligible for all tested ranges. An interesting trend of peak pressure correlated crank angle versus λ was also found in this study. [Display omitted] • A main by-product hydrogen resource of COG combustion in ICE is studied. • The by-product hydrogen composition and lean combustion effects are tested. • More H2 avails efficiency, lean limit extension, HC and CO2 reduction. • The by-product H2 engine gains better working capability than pure H2 engine. • CO for all conditions and NOx for ultra-lean conditions are negligible. [ABSTRACT FROM AUTHOR]

This paper proposed a feasible method for estimating the turbulent burning velocity of gasoline/hydrogen blends in a spark-ignited (SI) engine based on the cumulative heat release fraction, engine speed and engine geometry. The experiment was conducted on a naturally-aspirated port-injection gasoline engine equipped with a hydrogen injection system. The engine was run at 1400 rpm with different loads and hydrogen volume fractions in the intake gas. The test results showed that the addition of hydrogen benefited increasing the burning velocity and advancing the relevant crank angle for the peak burning velocity, due to the high burning and diffusion velocities of hydrogen. At 1400 rpm, a manifolds absolute pressure of 61.5 kPa and stoichiometric conditions, the peak burning velocity was raised from 11.6 to 12.3 and 14.6 m/s, and the relevant crank angle for the peak burning velocity was advanced from 21.0 to 14.0 and 8.6 oCA when the hydrogen volume fraction in the intake increased from 0% to 3% and 6%, respectively. Moreover, the effect of hydrogen addition on enhancing the burning velocity of a gasoline engine was more pronounced at low loads than that at high loads. • The charge burning velocity of H2-enriched engine is studied. • A way for estimating burning volicty in non-optical engine is proposed. • The H2-enriched engine acquired higher turbulent burning velocity. • The H2 is more effective for enhancing burning velocity at low loads. [ABSTRACT FROM AUTHOR]

[Display omitted] • The PC acting as igniter and oxidant supplier is used to control H2/O2 combustion. • The PC induced H2/O2 diffusive combustion is divided into four stages. • The ignition delay and combustion duration vary in opposite trend with φ G. • Transient of premix to diffusive combustion is decided by PC combustion intensity. • Enlarging orifice avails increasing pressure and combustion efficiency. The H2/O2 internal combustion is promising to be adopted as auxiliary power by combusting the wasted hydrogen in the upper stages under aerospace conditions. Concerning no inert gases participating the combustion, the control of H2/O2 heat release is a great challenge. This paper proposes to control the heat release by adopting an active pre-chamber (PC). All the combustion consumed oxygen is injected into the PC. The combustion of oxygen and small amount of pre-existed H2 in PC increases the PC pressure, enabling the hot reactant and massive oxygen to be injected into the main chamber (MC) to arrange the oxygen jet induced hydrogen diffusive combustion. The test was conducted on a constant volume combustion bomb (CVCB) to explore the effects of equivalence ratio (φ G) and orifice diameter on the diffusive H2/O2 combustion characteristics. The results showed that increasing φ G resulted in the decreased premix combustion fraction and prolonged combustion duration. The peak pressure of MC dropped with φ G indicating the ability of adjusting engine load by varying φ G. The heat release process could be controlled either by φ G or orifice diameter. Properly increasing the orifice diameter availed shortening the combustion duration and promoting the heat release efficiency. [ABSTRACT FROM AUTHOR]

As a hydrogen carrier, ammonia can suppress knock and enhance thermal efficiency of the hydrogen-fueled Wankel rotary engine (WRE), and achieve zero carbon emissions. This research established a three-dimensional fluid dynamics model coupled with detailed reaction kinetics of ammonia and hydrogen and verified it based on experiments. Incorporating 10% volume fraction of ammonia into the hydrogen-fueled WRE eliminates knock and decreases the excess air ratio (λ) from 1.8 to 1.4, effectively improving the indicated mean effective pressure (IMEP). The results indicate that when λ exceeds 1.4, flame propagation accelerates with higher concentration of the mixture. This enhances peak in-cylinder pressure and heat release rate, but it results higher NOx emissions. As λ varies from 1.8 to 1.4, NOx emission levels rise by 47.4%. At λ ≤ 1.2, the rapid flame propagation leads to short combustion duration, diminishing the power output. At this stage, the NO formation is dominated by H radicals, and the NOx production reaches its minimum value at λ of 1.0. In summary, the ammonia-hydrogen WRE achieves optimal performance at λ of 1.4 and ignition timing of −5 °CA after top dead center, the indicated thermal efficiency reaches 36.9% and the IMEP achieves 0.683 MPa. • The effect of ammonia addition on hydrogen-fueled WRE is analyzed. • The addition of ammonia is an effective way to prevent abnormal combustion. • The effects of excess air ratio on combustion and emission are analyzed. • The optimum ignition timing corresponding the optimal performance is given. • The optimum IMEP and ITE is obtained when the excess air ratio equals 1.4. [ABSTRACT FROM AUTHOR]

The energy of Wireless Sensor Network (WSN) in edge network is limited. In order to save energy, data bundling is proposed to reduce the energy consumed in setting up connection links by joining several packets into a single unit. However, although current data bundling schemes can reduce energy consumption, they will increase the delay of data routing, so it makes the multi-hop end to end delay a lot in WSN. Also, there is no appropriate solution to tackle the delayed growing problem caused by data bundling. And the energy consumption of the Acknowledgment (ACK) transmission is not comprehensively considered either. Regarding to those issues of previous researches, in this paper, a Data and ACK Bundling Scheme (DAB) is proposed to aggregate several data or ACK packets into a single unit to reduce the energy consumption as well as the end to end delay of the WSN. In the proposed DAB scheme, not only multiple packets but also ACK bundling into a single unit can reduce energy consumption. More importantly, the parameters of bundling technology are optimized from a global perspective in DAB scheme, so that WSN can not only improve the network lifetime, but also reduce the end to end delay which is impossible in previous studies. The theoretical analysis and experimental results illustrate that, while ensuring the reliability of data collection, our DAB scheme improves the energy efficiency by 29.03 % and reduces the delay by 22.29 % when compared with our traditional data collection scheme. [ABSTRACT FROM AUTHOR]

Adopting ammonia (NH 3) is considered a viable way to reduce carbon emissions. The combustion of NH 3 /air can be enhanced through the fuel dissociation strategy and the use of turbulent jet ignition (TJI). This study investigated the combustion of partially dissociated NH 3 ignited by active TJI. It can be found that the hydrogen (H 2) pre-chamber effectively enhances the combustion of partially dissociated NH 3 , and the appropriate rich pre-chamber equivalence ratio is beneficial for the main chamber ignition. The lean main chamber mixtures realize the flame ignition mechanism and show a lower ignition delay. The increase in dissociation ratio enhances the tolerance of ignition to turbulence and leads to flame ignition mechanism. The increase in dissociation ratio also enhances the inhibiting effect of additional nitrogen (N 2) on combustion, but the ignition mechanism and flame shape are not sensitive to the additional N 2. [Display omitted] • Combustion of partially dissociated NH 3 under active TJI conditions was studied. • Rich pre-chamber equivalence ratio is conducive to rapid ignition and combustion. • Lean main chamber mixture is beneficial for achieving flame ignition mechanism. • Dissociation of NH 3 enhances the tolerance of ignition to turbulence. [ABSTRACT FROM AUTHOR]

• Provide a comprehensive review of trajectory analysis for on-demand services. • Make a survey focusing on spatial-temporal demand and supply patterns. • Highlight the future research directions. With the development of information technique and wireless communication, a vast number of taxis' and ride-sharing cars' trajectory data that provide a rich and detailed source to study on-demand services have been collected. The increasing available trajectory data bring benefits and new challenges to the studies of on-demand services. To provide an overview of the benefits and challenges brought by the trajectory data, we provide a survey on recent studies of trajectory analysis (refer to analyzing trajectory datasets) for on-demand services in this paper. Our purposes are at least trifold. First, we highlight the value of trajectory data in understanding on-demand services and discuss the procedures of retrieving information for the demand part and the supply part from raw trajectory data. Second, we categorize related studies into three parts (the demand part, the supply part, and the mixed part) and review the significant findings. For the demand part, we focus on the models proposed for describing and explaining the spatial-temporal characteristics of observed trips. Methods or models proposed for describing trip statistics, scaling laws of trips, and dynamics of ridership are reviewed. We summarize four types of factors that influence the spatial-temporal patterns of demands. For the supply part, we focus on the models proposed for describing the spatial-temporal characteristics of available taxis/ride-sharing cars and modeling the behavior of drivers (i.e., passenger-search behavior and route choice behavior) to explain the spatial-temporal patterns of taxi/ride-sharing supplies. For the mixed part, we focus on studies that apply the uncovered demands/supplies patterns to design recommendation systems and pricing strategies. Third, we discuss the future directions on collecting/releasing trajectory data and future research directions to advance the understanding of on-demand services. [ABSTRACT FROM AUTHOR]

The coke oven gas (COG) which mainly consists of H2, CH4 and CO is a kind of feasible by-product hydrogen that could be applied by combustion plants. This paper conducted experiments and numerical calculations to explore the combustion properties of COG. The laminar burning velocity (LBV) and flame stability of COG with different CO/CH4/H2 fractions were firstly tested. Then, based on the LBV results, a new chemical kinetic model was proposed and a mixing rule for quick estimating the LBV of COG was acquired. The influences of different COG components on LBV were obtained. The peak LBV of COG could achieve 100.2 cm/s when the highest tested hydrogen portion in COG was adopted at an equivalence ratio of 1.2. Concerning its application in real combustion plants, the exhaust emissions of CO and NO from the COG final combustion products were also detected by an emissions analyzer. The results showed that raising the hydrogen fraction in COG availed reducing CO at rich conditions through lowering the carbon fraction. The NO emission gained the peak value around the equivalence ratio of 0.9, which was found to be generally raised with the hydrogen fraction due to the increased combustion temperature. • LBV of coke oven gas (COG) with different H2/CH4/CO ratio is measured. • A modified kinetic model and a fitting Eq. are proposed to estimate the LBV of COG. • COG containing more H2 and CO or less CH4 obtains higher LBV. • NO from COG final combustion products are raised with the H2 fraction. • Raising the H2 fraction in COG avails reducing CO emission at rich conditions. [ABSTRACT FROM AUTHOR]

This paper aims to numerically investigate the effects of high compression ratio (CR) on the performance of ammonia-hydrogen engines. In this work, four CRs from 10.7 to 13.7 with scanning spark timing (ST) from 28°CA to 0°CA BTDC were analyzed. The main results are as follows: As the CR increases, there is a trade-off relationship between the dissipation rate of turbulence and the turbulent kinetic energy (TKE). Initially, the TKE rises as the CR increases. As the CR continues to rise, the tendency for an increase in TKE diminishes, while the turbulent dissipation rate consistently rises. Additionally, there is an escalation in heat transfer loss. Therefore, there is a trend of rising and then falling in the flow velocity and turbulence intensity with the increase of the CR. Ammonia-hydrogen flame propagation is susceptible to temperature and flow field, and a high CR can improve ignition stability, shorten combustion duration, minimize cooling loss, and enhance output power. Unfortunately, the emission of NOx gradually rises as the CR increases. At high CR, the combustion performance is optimized by adjusting ST, and the maximum IMEP and ITE are 4 bar and 38.3 %, respectively. The ST for maximum braking torque (MBT) should be gradually delayed toward TDC as the CR increases. • As the compression ratio increases, the flow velocity first rises and then decreases. • The turbulent dissipation rate increases with increasing compression ratio. • A high compression ratio improves ignition stability and combustion velocity. • The NOx gradually increases with the increase of the compression ratio. • A high compression ratio improves the power and economy of NH3-H2 engines. [ABSTRACT FROM AUTHOR]

The effects of multiple operating parameters (including speed, valve timing, λ, manifold absolute pressure, spark timing, and hydrogen injection timing) on the coefficient of variation of indicated mean effective pressure ( C o V I M E P ) of a hydrogen-blended ammonia engine have not been adequately evaluated, which motivates this study. Specifically, C o V I M E P is decreased from exceeding 2.4 % to approximately 0.7 % when the speed increases from 1300 rpm to 2000 rpm. Optimizing valve timing keeps C o V I M E P below 0.8 % by improving the airflow exchange process, and the engine tends to realize lower C o V I M E P at close stoichiometric ratio conditions and low pumping loss. Furthermore, adjusting spark timing affects C o V I M E P by varying the ignition process's stability, with a combustion center of gravity around 9°CA ATDC being suggested. The hydrogen direct-injection timing influences the combustion process's instability by varying the mixture concentration gradient, and the late injection strategy allows the engine to achieve a C o V I M E P of less than 0.9 %. [Display omitted] • The cyclic variation of a hydrogen-blended ammonia engine is analyzed. • Combustion variations during the flame development and propagation are emphasized. • The influence mechanism of combustion process's instability on C o V I M E P is revealed. • C o V P m a x is more sensitive to fluctuations in the heat release process. • C o V P m a x may have exceeded 10 % when C o V I M E P is at a lower level. [ABSTRACT FROM AUTHOR]

The rapid growth of internet based ride-sharing brings great changes to residents' travel and city traffic. However, few studies had employed empirical data to examine the unique travel patterns of internet based ride-sharing trips. In this paper, we compare taxi trip records and internet based ride-sharing trip records provided by DiDi company. Results reveal many interesting findings that had never been reported before. From the viewpoint of service patterns, ride-sharing mainly increases supplies in hot areas and peak hours. By applying a non-negative matrix factorization method, we find that ride-sharing principally serves as an approach for commuting. So, as an effective supplement to traditional taxi service, it regulates spatial and temporal supply-demand imbalance, especially during morning and evening rush periods. From the viewpoint of individual behavior patterns, we use a clustering method to identify two kinds of internet based ride-sharing drivers. The first kind of drivers usually provides ride-sharing along daily home-work commuting. Trips served by these drivers have relatively constant origin-designation (OD) pairs. The second kind of drivers does not serve regularly and roams around the city even in working hours. Therefore, there are no constant OD pairs in their ride-sharing trips. Counterintuitively, we find that home-work commuting drivers account for only a small part of total drivers and they only serve a small number of commuting trips. In addition, internet based ride-sharing is not just traditional hitchhiking worked through mobile internet. We find that internet based ride-sharing drivers intend to make long distance trips, and they intend to detour further to pick up or drop off passengers than traditional hitchhike drivers since they are paid. All these findings are helpful for policy makers at all levels to make informed decisions about deployment of internet based ride-sharing service. This paper also verifies that big data analytics is particularly useful and powerful in the analysis of ride-sharing and taxi service patterns. [ABSTRACT FROM AUTHOR]

Hydrogen is a renewable fuel with excellent combustion characteristics. However, the direct use of hydrogen in existing engines faces obstacles such as abnormal combustion and high NOx emissions. This study proposes a strategy for controlling the combustion and emissions performance of a port-injection (PI) hydrogen internal combustion engine using ethanol direct injection (DI). The test conditions are 1000 rpm, 1500 rpm, and 2000 rpm respectively, the excess air coefficient is 1, 1.5, and 2, and 3%, 6%, and 9% ethanol is added. The results showed that the addition of ethanol can significantly reduce the pressure rise rate of the hydrogen engine and prolong CA0-10 and CA10-90. The addition of ethanol can promote the BMEP and BTE of the hydrogen engine. The addition of ethanol can reduce NOx emissions under lean burn conditions by 18%. The disadvantage is that the addition of ethanol increases the hydrocarbon emissions of hydrogen engines by about 50%, but the total amount is less. After the addition of ethanol, the flashback phenomenon of the hydrogen engine was significantly improved. [Display omitted] • Proposed ethanol-controlled hydrogen engine backfire strategy. • Studied the effect of ethanol addition on hydrogen engines. • The addition of ethanol increases CA0-10 and CA10-90. • The addition of ethanol improves engine BMEP and ITE. • The addition of ethanol reduces NOx emissions from hydrogen engines. [ABSTRACT FROM AUTHOR]

CO 2 (Carbon dioxide) dilution is a feasible way for controlling NOx (Nitrogen oxides) emissions and loads of the internal combustion engines. This paper investigated the effect of CO 2 dilution on the combustion and emissions characteristics of a hydrogen-enriched gasoline engine. The experiment was conducted on a 1.6 L spark-ignition engine with electronically controlled hydrogen and gasoline injection systems. At two hydrogen volume fractions of 0 and 3%, the CO 2 volume fraction in the intake was gradually increased from 0 to 4%. The fuel-air mixtures were kept at the stoichiometric. The experimental results demonstrated that brake mean effective pressure of the gasoline engine was quickly reduced after adopting CO 2 dilution. Comparatively, Bmep (Brake mean effective pressure) of the 3% hydrogen-enriched engine was gently decreased with the increase of CO 2 dilution level. Thermal efficiency of the 3% hydrogen-enriched gasoline engine was raised under properly increased CO 2 dilution levels. However, thermal efficiency of the pure gasoline engine was generally dropped after the CO 2 dilution. The addition of hydrogen could shorten flame development and propagation durations under CO 2 diluent conditions for the gasoline engine. Increasing CO 2 fraction in the intake caused the dropped NOx and raised HC (Hydrocarbon) emissions. Increasing hydrogen fraction in the intake could effectively reduce HC emissions under CO 2 diluent conditions. [ABSTRACT FROM AUTHOR]

Ammonia and hydrogen are two carbon-free alternative fuels for engines. Considering that there are few studies on improving an ammonia-hydrogen engine's lean combustion performance, this investigation based on an engine with the Miller cycle employs hydrogen direct injection (HDI) and NH 3 port injection and then proposes an adjustment strategy to vary the start of injection (SOI) of HDI for affecting the engine combustion process. When ammonia volume share (AVS) is greater than 50%, the engine shows poor performance. Nevertheless, the stratification effect of hydrogen jets may be used to elevate the hydrogen concentration around spark plug by properly delaying SOI and then creating the locally rich mixture with a high hydrogen share, which prominently promotes the flame kernel formation, shortens CA0-90, reduces C o V P m a x , and enables the engine to reach approximately 36% BTE. It is notable that very late SOI can slightly deteriorate the heat release process and lower engine performance. • Ammonia-hydrogen engines have poor combustion process under lean conditions. • A strategy to improve the lean combustion performance of the engine is proposed. • Effects of NH 3 –H 2 premixing and H 2 stratification effect on the engine are balanced. • Properly delaying SOI enhances the ignition and combustion process of the engine. [ABSTRACT FROM AUTHOR]

• LBV of H 2 /air blends diluted by EGR with varied H 2 O ratio and air was measured. • Both EGR and air dilution can effectively control LBV of H 2 /air. • NO emission can be reduced by increasing dilution ratio and water fraction in EGR. • H 2 emission first increases and then decreases with the increasing dilution ratio. • H 2 emission increases monotonically with the increase of water fraction in EGR. Lean combustion and exhaust gas recirculation (EGR) are key strategies for controlling NO and heat release process of hydrogen engines. This paper firstly compared these two strategies on combustion behaviors of hydrogen-air mixtures within dilution ratio ranges from 0 to 50%. Then, the water vapor effects in EGR on combustion of hydrogen-air mixtures are further investigated. All tests are conducted in a constant volume combustion vessel at the initial temperature of 373 K and pressure of 1 bar. CHEMKIN PRO is adopted to predict the hydrogen-air mixtures combustion behaviors under different conditions with one-dimensional premixed adiabatic planner flame model. The unburnt hydrogen concentration and the NO mole fraction in the final products were measured. The results show that laminar burning velocity decreases more obviously with the EGR ratio than air dilution ratio. EGR dilution has much obvious influence on reducing NO mole fraction in the final products. However, both dilution strategies adversely cause the increase of incompletely combusted H 2. To balance the NO control and unburned H 2 emission, 30% EGR rate with 20% water vapor fraction is recommended based on the testing ranges of this study. [ABSTRACT FROM AUTHOR]

The performance of a hydrogen-blended gasoline engine at lean and the wide open throttle conditions was investigated. A hydrogen port-injection system was adopted to introduce the hydrogen into each cylinder. The engine was operated at 1400 rpm and two hydrogen blending levels of 0% and 3%. The excess air ratio was raised from 1.00 to about 1.45 for a given hydrogen addition fraction. The test results demonstrated that the hydrogen blending contributed to the raised thermal efficiency and shortened flame development and propagation durations. An increased brake mean effective pressure was found after the hydrogen addition only at lean conditions. For both stoichiometric and lean conditions, the hydrogen blending was beneficial for reducing the engine cyclic variation. This provides a possibility to run a hydrogen-blended gasoline engine with the fully opened throttle position and control the engine torque only by adjusting the excess air ratio. Toxic emissions including HC, CO and particulate were reduced after the hydrogen blending. [ABSTRACT FROM AUTHOR]

This paper analyzed the combustion characteristic of a hydrogen-blended gasoline engine running at high loads and lean conditions. The cycle-to-cycle variation in indicated mean effective pressure, cylinder pressure during combustion, heat release fraction and exhaust emissions at different conditions were experimentally investigated. The results showed that the addition of hydrogen was able to improve the engine stability through reducing the cyclic variation in indicated mean effective pressure. Moreover, the fuel heat release rate and peak cylinder pressure were accelerated after the hydrogen addition. Both HC and CO emissions were reduced significantly after the hydrogen blending. NOx emissions were slightly increased after the hydrogen addition due to the high flame temperature of hydrogen. [ABSTRACT FROM AUTHOR]

The hydrogen-enriched gasoline engine is a promising option for future spark-ignited (SI) engines. However, the lack of quasi-dimensional combustion models for hydrogen-gasoline blends restrains the efficient prediction of its performance for varying operating conditions and hydrogen enrichment strategies. In this paper, a quasi-dimensional model was developed and validated for hydrogen-enriched gasoline engines with a new laminar flame speed expression. Correspondence between the calculated and experimentally measured engine combustion parameters was observed for different hydrogen addition levels. The comparison results indicated that the proposed quasi-dimensional model is suitable for engine performance prediction of hydrogen-enriched gasoline engines. [ABSTRACT FROM AUTHOR]

This paper studied the idling characteristic of a hydrogen-blended methanol engine under lean conditions and three hydrogen volume fractions in the intake of 0, 1% and 2%. The test was accomplished on a spark-ignition equipped with a hydrogen port-injection system. The test results showed that the addition of hydrogen contributed to the reduced fuel energy consumption at the idle condition. Because of the reduced engine idle speed, the engine fuel energy consumption rate was further reduced after increasing the excess air ratio of hydrogen-methanol-air mixtures. Both flame development and propagation periods were shortened and HC and CO emissions were reduced after the addition of hydrogen for the methanol engine at the idle and lean conditions. [ABSTRACT FROM AUTHOR]

Variable valve timing (VVT) and Miller cycle are advanced technologies employed to optimize engine performance by improving airflow exchange, which are seldom investigated based on the direct-injection (DI) hydrogen engine. The objective of this study is to assess the effects of intake valve closing (IVC) and exhaust valve opening (EVO) timing on the gas exchange performance, combustion, and emissions of a DI hydrogen engine, after which a synergistic control strategy of IVC and EVO timing is proposed. This work is conducted under wide-open throttle and 1500 rpm. The results indicate that the synergistic control of IVC and EVO timing can increase volumetric efficiency by more than 40%, enhance gas exchange performance, shorten combustion duration, and reduce cyclic variation, resulting in approximately 43.15% brake thermal efficiency. Furthermore, brake mean effective pressure can be increased by more than 60% and NO emissions are controlled to less than 20 ppm by optimizing valve timings. • A synergistic control strategy of intake and exhaust VVT is proposed. • The airflow exchange and combustion of a DI hydrogen engine are optimized. • The regulation of valve timings can improve gas exchange performance. • The engine can reach 43.15% maximum brake thermal efficiency. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposed a way for realizing the load control of a hydrogen-blended gasoline engine running at the wide open throttle (WOT) condition through lean combustion. The engine performance of the original gasoline engine and a 3% hydrogen-blended gasoline engine running at the WOT and lean conditions under various loads at a constant engine speed of 1400 rpm was compared. The experimental results showed that because of the reduced residual gas fraction and throttling loss, brake thermal efficiency of the 3% hydrogen-blended gasoline engine running at the WOT and lean conditions was obviously higher than that of the pure gasoline engine. The 3% hydrogen-blended gasoline engine running at the WOT and lean conditions produced much lower particulate and CO emissions than the original gasoline engine. Besides, NOx emissions at part load conditions were also reduced for the 3% hydrogen-blended gasoline engine running at the WOT and lean conditions. [Copyright &y& Elsevier]

Various solutions have been proposed to alleviate the shortage of parking places, including parking reservation systems and shared-parking systems. In such systems, drivers submit their parking requests in advance, especially their arrival and departure time. Then, the systems will reserve a proper parking spot for a driver if his/her parking request is accepted. However, the driver may arrive earlier or depart later, which may cause service failure. In shared-parking systems, the distributions of commuters' arrival/departure time have fixed patterns and may be learned based on historical data. Given the distributions of drivers' arrival/departure time, this paper proposes a Chance-constraint optimization model to solve the reservation and allocation problem for the shared-parking platform. This model aims to maximize the parking utilization level (i.e., the expectation of total occupied parking hours) and keep the service failure rate below a threshold value. We propose a rule-based mixed-integer linear programming to seek a satisfying solution to this model. Numerical tests show that our model performs better than baseline models in indicators such as parking utilization level and service failure rate. • We propose a reservation and allocation model which considers the uncertainty in drivers' arrival/departure time. • We aim to maximize the utilization level under the constraint that the service failure rate should be below a preselected threshold value. • A chance-constrained optimization model is formulated. We propose a rule-based mixed-integer linear programming to solve it. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposed a new combustion strategy for the spark-ignited (SI) engines. A gasoline engine was converted into a hybrid hydrogen–gasoline engine (HHGE) by adding a hydrogen injection system and a hybrid electronic control unit. Different from the conventional gasoline and hydrogen–enriched gasoline engines, the HHGE is fueled with the pure hydrogen at cold start to produce almost zero emissions, with the hydrogen–gasoline blends at idle and part loads to further improve thermal efficiency and reduce emissions, and with the pure gasoline to ensure the engine power output at high loads. Because the HHGE is fueled with the pure gasoline at high loads and speeds, experiments are only conducted at clod start, idle and part load conditions. Since lean combustion avails the further improvement of the engine performance, the HHGE was fueled with the lean mixtures in all tests. The experimental results showed that the hybrid hydrogen–gasoline engine was started successfully with the pure hydrogen, which produced 94.7% and 99.5% reductions in HC and CO emissions within 100s from the onset of the cold start, compared with the original gasoline engine. At an excess air ratio of 1.37 and idle conditions, indicated thermal efficiency of the 3% hydrogen–blended gasoline engine was 46.3% higher than that of the original engine. Moreover, the engine cyclic variation was eased, combustion duration was shortened and HC, CO and NOx emissions were effectively reduced for the hybrid hydrogen–gasoline engines. [Copyright &y& Elsevier]

Abstract: The gasoline engines always encounter the deteriorated thermal efficiency and increased toxic emissions at part load conditions. This paper investigated the effect of hydrogen/oxygen blends (hydroxygen) addition on the performance of a gasoline engine at different hydrogen volume fractions in the hydroxygen. The experiment was conducted on a 1.6 L gasoline engine equipped with a hydrogen and oxygen port injection system. A hybrid electronic control unit was adopted to control the spark timing and the injection timings and durations of hydrogen, oxygen and gasoline. The test was performed at a typical city driving speed of 1400 rpm, a manifolds absolute pressure of 61.5 kPa and two excess oxygen ratios of 1.00 and 1.20. The overall volume fraction of the hydroxygen in the total intake gas was fixed at 3%. The hydrogen volume fraction in the hydroxygen was raised from 0% to 100% by changing the injection durations of hydrogen and oxygen. The test results demonstrated that the engine thermal efficiency was obviously increased with the increase of hydrogen volume fraction in the hydroxygen. The fuel energy flow rate of the 3% hydroxygen-blended gasoline engine was lower than that of the original engine when the hydrogen volume fraction in the hydroxygen exceeded 70%. Both the flame development and propagation periods were shortened after the hydroxygen addition. HC, CO and NOx emissions were decreased with the increase of hydrogen volume fraction in the hydroxygen. But NOx emissions of the hydroxygen-blended engine were higher than those of the original engine for all hydrogen volume fractions in the hydroxygen. Moreover, at an excess oxygen ratio of 1.00, CO from the 3% hydroxygen-blended gasoline engine was also higher than that from the original engine. The reduced particulate emissions can be obtained only at relatively high hydrogen volume fractions in the hydroxygen. [Copyright &y& Elsevier]

Abstract: Because of the increased residual gas fraction and low combustion temperature, the traditional spark-ignited (SI) gasoline engines tend to encounter the dropped thermal efficiency and increased emissions at idle. This paper experimentally investigated the effects of hydrogen addition, cylinder cutoff, lean combustion and idle speed reduction on improving the combustion and emissions performance of gasoline engine at idle. The tests were conducted on a modified 1.6 L SI engine equipped with a hydrogen port-injection system and a self-developed hybrid electronic control unit (HECU). In the experiments, cylinder cutoff was realized by stopping the hydrogen and gasoline injections to the specified cylinders. The HECU was adopted to control the opening of idle bypass valve and spark timing at the reduced idle speed of 600 rpm. The test results showed that hydrogen addition, lean burn, cylinder cutoff and idle speed reduction were all effective on decreasing the engine fuel consumption at idle. Under the given test conditions, the combination of cylinder cutoff and hydrogen addition was the most effective, which reduced the fuel consumption by 33.25% at a hydrogen volume fraction in the intake of 2.87% and two-cylinder cutoff mode, compared with that of the original engine. Moreover, engine cyclic variation, HC and CO emissions were also decreased after hydrogen addition and cylinder cutoff. Because of the dropped combustion temperature, NO x emissions were decreased at the lean combustion and decreased idle speed. However, due to the increased residual gas fraction and weakened charge flow, HC emissions from the engine operating at an idle speed of 600 rpm and a hydrogen addition fraction of 3.20% were slightly higher than those from the original gasoline engine at idle. [Copyright &y& Elsevier]

Abstract: In this paper, the cyclic variation characteristics of a hydrogen-enriched gasoline engine under various operating conditions were experimentally investigated. The test was carried out on a modified four-cylinder gasoline engine equipped with an electronically controlled hydrogen injection system. A hybrid electronic control unit was developed to govern the injection timings and durations of hydrogen and gasoline to accomplish the on-line adjusting of the hydrogen blending level and excess air ratio. The engine was first run at idle condition with an idle speed of 790 rpm and then operated at 1400 rpm to investigate the cyclic variation in a hydrogen-blended gasoline engine at different hydrogen volume fractions in the total intake, excess air ratios, spark timings and manifolds absolute pressures. The test results demonstrated that the coefficient of variation in indicated mean effective pressure was distinctly decreased with the increase of hydrogen blending ratio. At 1400 rpm and a manifolds absolute pressure of 61.5 kPa, the relevant excess air ratio for the engine lean burn limit was extended from 1.45 to 2.55 when the hydrogen volume fraction in the intake was raised from 0% to 4.5%. Besides, for a specified hydrogen addition level, the coefficient of variation in indicated mean effective pressure was continuously increased but the coefficient of variation in the peak cylinder pressure was first raised and then decreased with the increase of excess air ratio. The experimental results also showed that hydrogen addition was more effective on reducing engine cyclic variation at low loads rather than at high loads. [Copyright &y& Elsevier]

Abstract: This paper compared the effects of hydrogen and hydrogen–oxygen blends (hydroxygen) additions on the performance of a gasoline engine at 1400 rpm and a manifolds absolute pressure of 61.5 kPa. The tests were carried out on a 1.6 L gasoline engine equipped with a hydrogen and oxygen injection system. A hybrid electronic control unit was applied to adjust the hydrogen and hydroxygen volume fractions in the intake increasing from 0% to about 3% and keep the hydrogen-to-oxygen mole ratio at 2:1 in hydroxygen tests. For each testing condition, the gasoline flow rate was adjusted to maintain the mixture global excess air ratio at 1.00. The test results confirmed that engine fuel energy flow rate was decreased after hydrogen addition but increased with hydroxygen blending. When hydrogen or hydroxygen volume fraction in the intake was lower than 2%, the hydroxygen-blended gasoline engine produced a higher thermal efficiency than the hydrogen-blended gasoline engine. Both the additions of hydrogen and hydroxygen help reduce flame development and propagation periods of the gasoline engine. HC emissions were reduced whereas NOx emissions were raised with the increase of hydrogen and hydroxygen addition levels. CO was slightly increased after hydrogen blending, but reduced with hydroxygen addition. [Copyright &y& Elsevier]

Abstract: The limited fossil fuel reserves and severe environmental pollution have pushed studies on improving the engine performance. This paper investigated the effect of hydrogen–oxygen blends (hydroxygen) addition on the performance of a spark-ignited (SI) gasoline engine. The test was performed on a modified SI engine equipped with a hydrogen and oxygen injection system. A hybrid electronic control unit was adopted to govern the opening and closing of hydrogen, oxygen and gasoline injectors. The standard hydroxygen with a fixed hydrogen-to-oxygen mole fraction of 2:1 was applied in the experiments. Three standard hydroxygen volume fractions in the total intake gas of 0%, 2% and 4% were adopted. For a given hydroxygen blending level, the gasoline injection duration was adjusted to enable the excess air ratio of the fuel-air mixtures to increase from 1.00 to the engine lean burn limit. Besides, to compare the effects of hydroxygen and hydrogen additions on the performance of a gasoline engine, a hydrogen-enriched gasoline engine was also run at the same testing conditions. The test results showed that the hydroxygen-blended gasoline engine produced higher thermal efficiency and brake mean effective pressure than both of the original and hydrogen-blended gasoline engines at lean conditions. The engine cyclic variation was eased and the engine lean burn limit was extended after the standard hydroxygen addition. The standard hydroxygen enrichment contributed to the decreased HC and CO emissions. CO from the standard hydroxygen-enriched gasoline engine is also lower than that from the hydrogen-enriched gasoline engine. But NOx emissions were increased after the hydroxygen addition. [Copyright &y& Elsevier]

Abstract: Because of the increased fuel-film effect and dropped combustion temperature, spark-ignited (SI) gasoline engines always expel large amounts of HC and CO emissions during the cold start period. This paper experimentally investigated the effect of hydrogen addition on improving the cold start performance of a gasoline engine. The test was carried out on a 1.6-L, four-cylinder, SI engine equipped with an electronically controlled hydrogen injection system. A hybrid electronic control unit (HECU) was applied to control the opening and closing of hydrogen and gasoline injectors. Under the same environmental condition, the engine was started with the pure gasoline and gasoline–hydrogen mixture, respectively. After the addition of hydrogen, gasoline injection duration was adjusted to ensure the engine to be started successfully. All cold start experiments were performed at the same ambient, coolant and oil temperatures of 17 °C. The test results showed that cylinder and indicated mean effective pressures in the first cycle were effectively improved with the increase of hydrogen addition fraction. Engine speed in the first 20 start cycles increased with hydrogen blending ratio. However, in later cycles, engine speed varied only a little with and without hydrogen addition due to the adoption of close loop control on engine speed. Because of the low ignition energy and high flame speed of hydrogen, both flame development and propagation durations were shortened after hydrogen addition. HC and CO emissions were dropped markedly after hydrogen addition due to the enhanced combustion process. When the hydrogen flow rate increased from 0 to 2.5 and 4.3 L/min, the instantaneous peak HC emissions were sharply reduced from 57083 to 17850 and 15738 ppm, respectively. NOx emissions were increased in the first 5 s and then reduced later after hydrogen addition. [Copyright &y& Elsevier]

Abstract: To reduce the fuel consumption and emissions of spark-ignited (SI) engines, hydrogen enrichment was used to improve the performance of a lean burn SI engine operating at low speed and load conditions. A hydrogen port-injection system was mounted on the intake manifolds to introduce hydrogen into the intake ports sequentially while keeping the original gasoline injection system unchanged. A hybrid electronic control unit (HECU) was adopted to control injection timings and durations of gasoline and hydrogen, accomplishing four excess air ratios of 1.00, 1.18, 1.43 and 1.67 and three hydrogen volume fractions in the intake of 3%, 5%, 8%. The experimental results showed that engine brake thermal efficiency and torque output were increased, combustion durations were shortened, cyclic variation and HC emissions were reduced, but NO x emissions were increased with the increase of hydrogen addition. CO emission was also reduced under lean conditions with hydrogen enrichment. [Copyright &y& Elsevier]

Abstract: Because of the low combustion temperature and high throttling loss, SI (spark-ignited) engines always encounter dropped performance at low load conditions. This paper experimentally investigated the co-effect of cylinder cutoff and hydrogen addition on improving the performance of a gasoline-fueled SI engine. The experiment was conducted on a modified four-cylinder SI engine equipped with an electronically controlled hydrogen injection system and a hybrid electronic control unit. The engine was run at 1400 rpm, 34.5 Nm and two cylinder cutoff modes in which one cylinder and two cylinders were closed, respectively. For each cylinder closing strategy, the hydrogen energy fraction in the total fuel was increased from 0% to approximately 20%. The test results demonstrated that engine indicated thermal efficiency was effectively improved after cylinder cutoff and hydrogen addition, which rose from 34.6% of the original engine to 40.34% of the engine operating at two-cylinder cutoff mode and . Flame development and propagation periods were shortened with the increase of the number of closed cylinders and hydrogen blending ratio. The total cooling loss for all working cylinders, and tailpipe HC (hydrocarbons), CO (carbon monoxide) and CO2 (carbon dioxide) emissions were reduced whereas tailpipe NO x (nitrogen oxide) emissions were increased after hydrogen addition and cylinder closing. [ABSTRACT FROM AUTHOR]

Abstract: Reducing idle speed is an effective way for decreasing engine idle fuel consumption. Unfortunately, due to the increased residual dilution and dropped combustion temperature, spark-ignited (SI) gasoline engines are prone to suffer high cyclic variation and even stall at low idle speeds. This paper investigated the effect of hydrogen addition on the performance of an SI gasoline engine at reduced idle speeds of 600, 700 and 800 rpm. The test results shows that cyclic variation was raised with the decrease of idle speed but reduced obviously with the increase of hydrogen energy fraction . Decreasing idle speed and adding hydrogen were effective for reducing engine idle fuel consumption. The total fuel energy flow rate was effectively dropped from 30.8 MJ/h at 800 rpm and  = 0% to 17.6 MJ/h at 600 rpm and  = 19.9%. Because of the dropped fuel energy flow rate causing the reduced combustion temperature, both cooling and exhaust losses were markedly reduced after decreasing idle speed and adding hydrogen. HC and CO emissions were dropped with the increase of , but increased after reducing idle speed. However, NOx emissions were decreased after reducing idle speed and adding hydrogen, due to the dropped peak cylinder temperature. [ABSTRACT FROM AUTHOR]

Abstract: Regarding the limited fossil fuel reserves, the renewable ethanol has been considered as one of the substitutional fuels for spark ignition (SI) engines. But due to its high latent heat, ethanol is usually hard to be well evaporated to form the homogeneous fuel–air mixture at low temperatures, e.g., at idle condition. Compared with ethanol, hydrogen possesses many unique combustion and physicochemical properties that help improve combustion process. In this paper, the performance of a hydrogen-enriched SI ethanol engine under idle and stoichiometric conditions was investigated. The experiment was performed on a modified 1.6 L SI engine equipped with a hydrogen port-injection system. The ethanol was injected into the intake ports using the original engine gasoline injection system. A self-developed hybrid electronic control unit (HECU) was adopted to govern the opening and closing of hydrogen and ethanol injectors. The spark timing and idle bypass valve opening were governed by the engine original electronic control unit (OECU), so that the engine could operate under its original target idle speed for each testing point. The engine was first fueled with the pure ethanol and then hydrogen volume fraction in the total intake gas was gradually increased through increasing hydrogen injection duration. For a specified hydrogen addition level, ethanol flow rate was reduced to keep the hydrogen–ethanol–air mixture at stoichiometric condition. The test results showed that hydrogen addition was effective on reducing cyclic variations and improving indicated thermal efficiency of an ethanol engine at idle. The fuel energy flow rate was reduced by 20% when hydrogen volume fraction in the intake rose from 0% to 6.38%. Both flame development and propagation periods were shortened with the increase of hydrogen blending ratio. The heat transfer to the coolant was decreased and the degree of constant volume combustion was enhanced after hydrogen addition. HC and CO emissions were first reduced and then increased with the increase of hydrogen blending fraction. The acetaldehyde emission from the hydrogen-enriched ethanol engine is lower than that from the pure ethanol engine. However, the addition of hydrogen tended to increase NO x emissions from the ethanol engine at idle and stoichiometric conditions. [Copyright &y& Elsevier]

Abstract: The addition of hydrogen is an effective way for improving the gasoline engine performance at lean conditions. In this paper, an experiment aiming at studying the effect of hydrogen addition on combustion and emissions characteristics of a spark-ignited (SI) gasoline engine under various loads and lean conditions was carried out. An electronically controlled hydrogen port-injection system was added to the original engine while keeping the gasoline injection system unchanged. A hybrid electronic control unit was developed and applied to govern the spark timings, injection timings and durations of hydrogen and gasoline. The test was performed at a constant engine speed of 1400rpm, which could represent the engine speed in the typical city-driving conditions with a heavy traffic. Two hydrogen volume fractions in the total intake of 0% and 3% were achieved through adjusting the hydrogen injection duration according to the air flow rate. At a specified hydrogen addition level, gasoline flow rate was decreased to ensure that the excess air ratios were kept at 1.2 and 1.4, respectively. For a given hydrogen blending fraction and excess air ratio, the engine load, which was represented by the intake manifolds absolute pressure (MAP), was increased by increasing the opening of the throttle valve. The spark timing for maximum brake torque (MBT) was adopted for all tests. The experimental results demonstrated that the engine brake mean effective pressure (Bmep) was increased after hydrogen addition only at low load conditions. However, at high engine loads, the hybrid hydrogen–gasoline engine (HHGE) produced smaller Bmep than the original engine. The engine brake thermal efficiency was distinctly raised with the increase of MAP for both the original engine and the HHGE. The coefficient of variation in indicated mean effective pressure (COVimep) for the HHGE was reduced with the increase of engine load. The addition of hydrogen was effective on improving gasoline engine operating instability at low load and lean conditions. HC and CO emissions were decreased and NOx emissions were increased with the increase of engine load. The influence of engine load on CO2 emission was insignificant. All in all, the effect of hydrogen addition on improving engine combustion and emissions performance was more pronounced at low loads than at high loads. [Copyright &y& Elsevier]

Abstract: Hydrogen addition is an effective way for improving the performance of spark-ignited (SI) engines at stoichiometric and especially lean conditions. Spark timing also heavily influences the SI engine performance. This paper experimentally investigated the effect of spark timing on performance of a hydrogen-enriched gasoline engine at lean conditions. The experiment was carried out on a four-cylinder, port-injection gasoline engine which was modified to be an electronically controlled hybrid hydrogen–gasoline engine (HHGE) by adding a hydrogen port-injection system on the intake manifolds while keeping the original gasoline injection system unchanged. A hybrid electronic control unit (HECU) was developed to govern the injection timings and durations of hydrogen and gasoline to enforce the timely mixing of hydrogen and gasoline in the intake ports at the expected blending levels and excess air ratios. During the test, the engine speed was fixed at 1400rpm and the manifolds absolute pressure (MAP) was kept at 61.5kPa. The hydrogen volume fraction in the intake was increased from 0% to 3% through adjusting the hydrogen injection duration. For a specified hydrogen addition level, gasoline injection duration was reduced to ensure the engine operating at two excess air ratios of 1.2 and 1.4, respectively. The spark timing for a specified hydrogen addition level and excess air ratio was varied from 20 to 50 °CA BTDC with an interval of 2 °CA. The test results showed that the indicated mean effective pressure (Imep) first increased and then decreased with the increase of spark advance. The optimum spark timing for the max. Imep (OST) was retarded for the HHGE at a specified excess air ratio. The max. indicated thermal efficiency appeared at the OST. Flame development period was shortened whereas flame propagation period was prolonged with the decrease of spark advance. The coefficient of variation in indicated mean effective pressure generally gained its minimum value at the OST. HC and NOx emissions were continuously decreased with the retarding of spark timing. However, the effect of spark timing on CO emission was found insignificant. [Copyright &y& Elsevier]

Abstract: Lean combustion is an effective way for improving the spark-ignited (SI) engine performance. Unfortunately, due to the narrow flammability of gasoline, the pure gasoline-fueled engines sometimes suffer partial burning or misfire at very lean conditions. Hydrogen has many excellent combustion properties that can be used to extend the gasoline engine lean burn limit and improve the gasoline engine performance at lean conditions. In this paper, a 1.6L port fuel injection gasoline engine was modified to be a hybrid hydrogen–gasoline engine (HHGE) fueled with the hydrogen–gasoline mixture by mounting an electronically controlled hydrogen injection system on the intake manifolds while keeping the original gasoline injection system unchanged. A self-developed hybrid electronic control unit (HECU) was used to flexibly adjust injection timings and durations of gasoline and hydrogen. Engine tests were conducted at 1400rpm and a manifolds absolute pressure (MAP) of 61.5kPa to investigate the performance of an HHGE at lean burn limits. Three hydrogen volume fractions in the total intake gas of 1%, 3% and 4.5% were adopted. For a specified hydrogen volume fraction, the gasoline flow rate was gradually reduced until the engine reached the lean burn limit at which the coefficient of variation in indicated mean effective pressure (COVimep) was 10%. The test results showed that COVimep at the same excess air ratio was obviously reduced with the increase of hydrogen enrichment level. The excess air ratio at the lean burn limit was extended from 1.45 of the original engine to 2.55 of the 4.5% HHGE. The engine brake thermal efficiency, CO, HC and NO x emissions at lean burn limits were also improved for the HHGE. [Copyright &y& Elsevier]

Abstract: Due to the narrow flammability of gasoline, pure gasoline-fueled spark-ignited (SI) engines always encounter partial burning or even misfire at lean conditions. Gasoline engines tend to suffer poor combustion and expel large emissions at idle conditions because of the high variation in the intake charge and low combustion temperature. Comparatively, hybrid hydrogen engines (HHE) fueled with the mixtures of hydrocarbon fuels and hydrogen seem to achieve lower emissions and gain higher thermal efficiencies than the original hydrocarbon-fueled engines due to the wide flammability and high flame speed of hydrogen. Since a HHE only requires a small amount of hydrogen, it also removes concerns about the high production and storage costs of hydrogen. This paper introduced an experiment conducted on a four-cylinder SI gasoline engine equipped with a hydrogen port-injection system to explore the performance of a hybrid hydrogen–gasoline engine (HHGE) at idle and lean conditions. The injection timings and durations of hydrogen and gasoline were governed by a hybrid electronic control unit (HECU) developed by the authors, which can be adjusted freely according to the commands from a calibration computer. During the test, hydrogen flow rate was varied to ensure that hydrogen volume fraction in the intake was constantly kept at 3%. For the specified hydrogen addition level, gasoline flow rate was reduced to make the engine operate at idle and lean conditions with various excess air ratios. The test results demonstrated that cyclic variations in engine idle speed and indicated mean effective pressure were eased with hydrogen enrichment. The indicated thermal efficiency was obviously higher for the HHGE than that for the original gasoline engine at idle and lean conditions. The indicated thermal efficiency at an excess air ratio of 1.37 was increased from 13.81% for the original gasoline engine to 20.20% for the HHGE with a 3% hydrogen blending level. Flame development and propagation periods were also evidently shortened after hydrogen blending. Moreover, HC, CO and NOx emissions were all improved after hydrogen enrichment at idle and lean conditions. Therefore, the HHE methodology is an effective and promising way for improving engine idle performance at lean conditions. [Copyright &y& Elsevier]

Abstract: Hydrogen has many excellent combustion properties that can be used for improving combustion and emissions performance of gasoline-fueled spark ignition (SI) engines. In this paper, an experimental study was carried out on a four-cylinder 1.6L engine to explore the effect of hydrogen addition on enhancing the engine lean operating performance. The engine was modified to realize hydrogen port injection by installing four hydrogen injectors in the intake manifolds. The injection timings and durations of hydrogen and gasoline were governed by a self-developed electronic control unit (DECU) according to the commands from a calibration computer. The engine was run at 1400rpm, a manifold absolute pressure (MAP) of 61.5kPa and various excess air ratios. Two hydrogen volume fractions in the total intake of 3% and 6% were applied to check the effect of hydrogen addition fraction on engine combustion. The test results showed that brake thermal efficiency was improved and kept roughly constant in a wide range of excess air ratio after hydrogen addition, the maximum brake thermal efficiency was increased from 26.37% of the original engine to 31.56% of the engine with a 6% hydrogen blending level. However, brake mean effective pressure (Bmep) was decreased by hydrogen addition at stoichiometric conditions, but when the engine was further leaned out Bmep increased with the increase of hydrogen addition fraction. The flame development and propagation durations, cyclic variation, HC and CO2 emissions were reduced with hydrogen addition. When excess air ratio was approaching stoichiometric conditions, CO emission tended to increase with the addition of hydrogen. However, when the engine was gradually leaned out, CO emission from the hydrogen-enriched engine was lower than the original one. NO x emissions increased with the increase of hydrogen addition due to the raised cylinder temperature. [Copyright &y& Elsevier]

Abstract: With regard to the improvement of efficiency, combustion stability, and emissions in a gasoline engine at idle condition, an experimental study aimed at improving engine idle performance through hydrogen addition was carried out on a 4-cylinder gasoline-fueled spark ignited (SI) engine. The engine was modified to be fueled with the mixture of gasoline and hydrogen injected into the intake ports simultaneously. A self-developed electronic control unit (DECU) was dedicatedly used to control the injection timings and injection durations of gasoline and hydrogen. Other parameters, such as spark timing and idle valve opening, were controlled by the original engine electronic control unit (OECU). Various hydrogen enrichment levels were selected to investigate the effect of hydrogen addition on engine speed fluctuation, thermal efficiency, combustion characteristics, cyclic variation and emissions under idle and stoichiometric conditions. The experimental results showed that thermal efficiency, combustion performance, NO x emissions are improved with the increase of hydrogen addition level. The HC and CO emissions first decrease with the increasing hydrogen enrichment level, but when hydrogen energy fraction exceeds 14.44%, it begins to increase again at idle and stoichiometric conditions. [Copyright &y& Elsevier]

The present work proposes the application of CH 4 and H 2 synergy to improve the performance of the Wankel rotary engine (WRE). The whole work was experimentally conducted at 1500 r/min. The results indicate that CH 4 WRE can achieve similar power and significantly higher thermal efficiency than gasoline WRE based on quantitative control, with a maximum absolute efficiency improvement of 11.4%. At the same time, it also can achieve 64% and 77% maximum reduction of CO and NO emissions, respectively. CH 4 –H 2 synergy can further improve the performance of CH 4 -fueled WRE, which can broaden the lean flammability limits and make qualitative control application possible. Compared with CH 4 WRE with quantitative control, qualitative control hybrid fuel WRE can achieve a maximum relative improvement of 6.54% in brake thermal efficiency and significantly reduced NO and CO emissions. However, the extent of qualitative control is limited by cyclic variation. Overall, CH 4 –H 2 synergy can be a potential alternative to elevate the performance of WRE, the key to which is the reasonable match of synergy level and qualitative control extent. • Comparison of performances between CH4 and gasoline Wankel rotary engines. • CH4 has significant advantages in efficiency, CO and NO emission than gasoline. • CH4–H2 synergy can further improve the performance of the CH4 Wankel rotary engine. • Blending H2 coupling qualitative control is a good load control model in CH4 WRE. [ABSTRACT FROM AUTHOR]

Internal combustion engines fueled with mixtures of hydrogen (H 2) and ammonia (NH 3) are potential power devices for reducing carbon emissions. To improve the ignition and combustion performance of NH 3 /H 2 , turbulent jet ignition (TJI) can be used. This study aims to investigate NH 3 /H 2 /air combustion under TJI modes at low equivalence ratios. Considering that the adoption of the scavenging system is beneficial for improving the reactivity of the pre-chamber, the effect of active TJI with scavenging is also explored. The results show that injecting 1.2 times the initial mixture volume of air is optimal for scavenging, and the scavenging effect becomes significant as the NH 3 fraction increases. Using conventional active TJI and active TJI with scavenging effectively improves ignition performance and flame propagation, reducing sensitivity to the equivalence ratio compared to passive TJI mode. Although the adoption of active TJI modes improves the lean flammability limit of NH 3 /H 2 , weak flame propagation may occur in the early stage of combustion under ultra-lean conditions. Appropriately increasing the injection of auxiliary H 2 can effectively improve this phenomenon. • Scavenging in the pre-chamber is conducive to the improvement of jet generation. • H 2 -assisted pre-chamber reduces the sensitivity of combustion to equivalence ratio. • Weak flame propagation may occur in the early combustion of ultra-lean mixtures. • An appropriate increase of H 2 injection can improve the initial flame propagation. [ABSTRACT FROM AUTHOR]

To achieve sustainable transportation, ammonia (NH 3) and hydrogen (H 2) should be applied in internal combustion engines. The adoption of turbulent jet ignition (TJI) can improve ignition and combustion stability. The present study aims to explore the combustion characteristics of NH 3 /H 2 /air adopting TJI, and the effect of nitrogen (N 2) dilution on factors such as ignition mechanism and flame propagation process was analyzed. The results indicate that N 2 dilution worsens the combustion of NH 3 /H 2 /air. When the H 2 volume fraction is 50%, a dilution ratio of 30% can increase the ignition delay and combustion duration by 3–6 times. With the increase of the dilution ratio, sensitivities of ignition delay and combustion duration to dilution ratio are enhanced in both passive TJI and active TJI modes. Compared to passive TJI, the injection of auxiliary gas in active TJI mode reduces the sensitivity of jet velocity to dilution, which can accelerate the early stage of flame development. However, the high turbulence intensity provided by active TJI makes the ignition position closer to the bottom and causes an extended final stage of combustion. For ultra-low reactivity mixtures, the active TJI with the scavenging system can provide sufficient ignition energy, but ignition occurs after prolonged accumulation of heat and radicals, as well as dissipation of turbulence. • Effects of N 2 dilution on NH 3 /H 2 /air combustion with TJI is studied. • H 2 -assisted TJI reduces the sensitivity of ignition performance to dilution. • High-speed jet suppresses flame propagation near the orifice in active TJI mode. • Scavenging can improve the flammability limit for N 2 diluted NH 3 /H 2. • Weak flame may occur in the early combustion for low reactivity mixture. [ABSTRACT FROM AUTHOR]

Ammonia (NH 3) and hydrogen (H 2) mixture are expected to replace traditional fossil fuels in the transportation industry to achieve zero-carbon emissions. Adopting turbulent jet ignition (TJI) is a reliable way to enhance the ignition and combustion of NH 3 /H 2. The present study aims to explore the effects of initial pressure and temperature on the ignition and combustion characteristics of NH 3 /H 2 ignited by TJI. It can be found that the increased initial pressure reduces the jet velocity. Due to the joint effect of weakened turbulence and inherent flame propagation characteristics caused by the elevated pressure, the combustion duration is extended. However, the ignition performance can be enhanced by increasing the initial pressure. Improvement is reflected in the emergence of flame ignition mechanisms and the obvious radial propagation of jet flames in early development. The increase in initial temperature slightly increases the peak jet velocity, while the auxiliary H 2 in active mode will reduce the sensitivity of jet velocity to the initial temperature. Although the increased initial temperature has shown the promotion for achieving rapid ignition and combustion, there is no significant improvement in the ignition mechanism, the ignition is caused by accumulated heat and radicals provided by the reacted jet. • Effects of pressure and temperature on NH 3 /H 2 combustion in TJI mode were studied. • Increased pressure is beneficial for achieving the flame ignition mechanism. • A more obvious radial jet flame propagation is promoted by the elevated pressure. • Injected auxiliary H 2 reduces the sensitivity of jet generation to temperature. [ABSTRACT FROM AUTHOR]

The hydrogen-fueled Wanke rotary engine is a promising power system that has both high power and eco-friendly properties. This work investigated the effect of ignition timing on a dual-spark plugs synchronous-ignition hydrogen-fueled Wankel rotary engine under low speed, part load and lean combustion. The results show that with delaying the ignition timing, CA0-10 is shortened first and then lengthened and CA10-90 is consistently shortened. When the CA50 is located between 35 and 40°CA ATDC, the maximum brake torque can be realized. Besides, the selection of ignition timing needs to consider the "trade-off" relationship between the combustion phase and corresponding in-cylinder pressure. The maximum brake torque ignition timing is between 5 and 10°CA ATDC. And there is also a "trade-off" relationship between stability and thermal load when ignition timing is selected. In addition, HC and NO emissions will not become the problem limiting the power performance of hydrogen-fueled Wankel rotary engine under this operating condition. • A modified synchronous ignition hydrogen Wankel rotary engine was used. • The effect of ignition timing on performance of rotary engine was studied. • The power depends mainly on the in-cylinder pressure near 135°CA ATDC. • Selecting ignition timing needs to weigh the stability and thermal load. • Suitable ignition timing makes CA50 located between 35 and 40°CA ATDC. [ABSTRACT FROM AUTHOR]

Abstract: This paper investigated the emissions performance of a passenger car powered by the hybrid hydrogen–gasoline engine under the New European Driving Cycle. The hydrogen was produced from an onboard water electrolysis hydrogen generator fixed in the trunk. The test results demonstrated that, when the engine was started with pure hydrogen for the first 7s and fueled with the pure gasoline after 11s from the onset of the cold start, CO and HC emissions were reduced by 62.1% and 64.1%, respectively. The vehicle emissions performance could be improved from the Euro-II emissions standard of the original vehicle to the Euro-IV emissions standard of the hybrid hydrogen–gasoline engine-powered vehicle. [Copyright &y& Elsevier]

• A zero-carbon hybrid powertrain based on an ammonia-hydrogen ICE is proposed. • Fuel supply strategy based on ammonia suppression hydrogen combustion knock is established. • A simulation model of the ammonia-hydrogen hybrid system is developed. • Ammonia-hydrogen hybrid systems are superior in both performance and economy. In the context of carbon neutrality, high efficiency, low carbon, and zero environmental impact have become an essential development direction of internal combustion engines (ICEs). Hydrogen energy has the advantage of having a high calorific value. It also has zero carbon emissions and is considered one of the significant alternative fuels for ICEs. Moreover, ammonia has a high octane number and has an anti-knock effect, which facilitates the mitigation of knock in hydrogen ICEs and potentially mitigates the negative impact of knock on engine volume power. Scholars have carried out some explorations on ammonia-hydrogen ICEs (AHICE), which have been applied in marine power systems. It is anticipated that AHICE will become one of the most significant development directions in the field of vehicle power systems in the future. However, there are still some problems with using AHICEs in passenger cars. The proposed work presented a zero-carbon hybrid power system based on an AHICE. Specifically, the external characteristics curve and power output boundary were obtained by bench experiments of the ICE under wide open throttle (WOT) conditions and diverse engine speeds and λ. Indeed, a hybrid system model consisting of an AHICE and a power battery was built where the AHICE was used to respond to the demanded power and the power battery was used to provide additional power and store the electrical energy converted from braking. Incidentally, an engine control strategy was developed to expand the knock limit and power boundary by dynamically adjusting the ammonia-hydrogen volume ratio. Finally, a hybrid power system simulation model was established based on MATLAB/Simulink. The CLTC-P and WLTC simulation results demonstrated that the zero-carbon hybrid system which comprised AHICE and power battery can work in the high efficiency area. The AHICE demonstrates lower fuel consumption while satisfying power requirements. This work provides a promising route to zero-carbon hybrid technology for the passenger car industry facing the challenge of carbon neutrality. [ABSTRACT FROM AUTHOR]

Hydrogen internal combustion engines (ICE) will play an important role in reducing carbon emissions, but low power density and abnormal combustion problems are the main obstacles restricting the promotion of hydrogen ICE. Ammonia is a low-reactivity renewable fuel. The purpose of this study is to study the effect of different ammonia-added volume fractions on hydrogen ICE. In this experimental study, the combustion and emission characteristics of an engine fueled by a hydrogen/ammonia mixture were evaluated at part-load operating conditions. The experiment was carried out on a modified engine, the engine speed was 1300 rpm, the absolute pressure of the manifold was 61 kPa, and the volume fraction of ammonia added was 5.2%, 7.96%, and 10.68%, respectively. The test results show that the addition of ammonia changes the combustion characteristics of hydrogen. As the volume fraction of ammonia added increases, the flame development period and flame propagation period are both prolonged, and the peak heat release rate decreases. The addition of ammonia increases the power of the engine and reduces the indicated thermal efficiency. At the ignition timing of the maximum braking torque, as the volume fraction of ammonia added increases, the indicated mean effective pressure and indicated thermal efficiency increase. Adding ammonia volume fraction has little effect on Nitrogen oxides (NOx) emissions, and NOx emissions gradually increase with the delay of ignition timing. • Study the effect of ammonia addition on hydrogen-fueled engines. • The addition of ammonia improves the IMEP of hydrogen-fueled engines. • The addition of ammonia reduces the heat release rate of hydrogen-fueled engines. • Ammonia addition fraction has less effect on NOx emission. [ABSTRACT FROM AUTHOR]