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Ammonia is gaining attention as a non-carbon environmental-friendly fuel due to its superior storage capability compared to hydrogen. However, its high minimum ignition energy and slow laminar flame speed make it unsuitable for application in combustion-based energy conversion devices. In particular, when applied to internal combustion engines, issues such as combustion instability and limitations in operational range exist. Therefore, the intention is to address these issues by adding hydrogen, which has a wider flammable range and a faster laminar flame speed, to ammonia. In this study, the extension of the operable range of ammonia-fueled spark ignition engine by hydrogen addition was mainly discussed. Ammonia was injected directly in the cylinder and hydrogen was supplied into the intake port. The result showed that operable range of ammonia fueled combustion with hydrogen addition could be extended from 0.2 to 1.4 MPa with relatively stable combustion, i.e. CoV of gIMEP <5 %, except for one case. Moreover, under the BMEP 1 MPa load condition, hydrogen addition improved brake thermal efficiency (BTE) as 4.7 % and unburned ammonia also reduced by 25 %. [Display omitted] • About 5 % of hydrogen addition stabilize the ammonia engine under medium and high load. • Operable loads are extended with hydrogen addition. • Combustion duration became shorter as the load higher. • Improved combustion efficiency reduces unburned ammonia. [ABSTRACT FROM AUTHOR]

In this study, the effects of varying excess air ratios on a 2.0 L naturally aspirated (NA) hydrogen-fueled spark ignition (SI) engine were evaluated under low-load conditions by using port fuel injection (PFI) and direct injection (DI) systems. The engine speeds chosen were 1,200 rpm and 2,000 rpm. The excess air ratio was varied between 1.0 and 2.7 by controlling the throttle and hydrogen fuel rate under a brake mean effective pressure of 0.4 MPa. The combustion mechanism, net indicated thermal efficiency (ITE), brake thermal efficiency (BTE), gas exchange efficiency, mechanical efficiency, and engine-out nitrogen oxide (NOx) emissions were mainly discussed. The results indicated that the main combustion duration of PFI was shorter than that of DI due to its homogeneity, and the ITE values of PFI were similar or slightly lower than those of DI. However, as the mechanical efficiency of DI was higher than that of PFI, the BTE values of DI were always higher than those of PFI (the maximum BTE was 39.7 %). The NOx reduction potential of DI was superior to that of PFI due to stratified combustion, and its lowest value was 0.03 g/kWh. In addition, as the CO2 concentration in the exhaust gas increased, the brake-specific CO2 reduced (< 5.71 g/kWh). [ABSTRACT FROM AUTHOR]

Hydrogen is advantageous for use in internal combustion engines (ICEs) because of its high laminar flame speed and carbon-neutral characteristics. However, because of its low minimum ignition energy, abnormal combustions such as back-fire, pre-ignition, and knocking hinder its efficient supply as a fuel to ICEs under near stoichiometric conditions. Hence, in this study, the effect of various excessive air ratios (λ) on the performance of a hydrogen-fueled spark ignition engine using port fuel injection (PFI) was evaluated under wide-open throttle conditions. After determining the highest limit for the maximum brake torque, a hydrogen direct injection (DI) system was applied under the same λ and abnormal combustion limits to improve the brake power (BP). Results show that at 1,500 rpm, a maximum BP of 14.7 kW was achieved under a λ value of 1.4 with PFI; however, it can be increased up to 21.1 kW using DI with the same brake thermal efficiency under a compression ratio of 14. [ABSTRACT FROM AUTHOR]

Dual-fueled combustion, using high and low reactivity fuels simultaneously, is a promising combustion method that enables reduction of nitrogen oxides (NOx) emission. However, the total amount of NOx emissions in the exhaust gas is strongly influenced by the overall excessive air ratio (lambda) of air—fuel mixture. Thus, lean mixture condition is important for NOx emissions although RCCI operating condition is applied. In addition, not only reduction of emissions, but improvement in BTE requires the boost pressure to be increased. Thus, variations in boost pressure via a controlling turbocharger system was evaluated under general dual-fueled combustion and RCCI conditions using diesel and natural gas fuels while tracing emissions and BTE. The results indicated that higher boost pressure was more effective on RCCI condition in reducing NOx emissions and enhancing BTE and turbocharging system efficiency with lower carbon dioxides, compared to those of general dual-fueled combustion condition. Especially, turbocharger efficiency of dual-fueled combustion was higher than that of diesel single-fueled combustion related with composition of exhaust gas and exhaust gas temperatures. [ABSTRACT FROM AUTHOR]

In this study, a high-load expansion strategy was investigated by varying the effective compression ratio (CR) using the variable valve duration (VVD) method during combustion in a gasoline/diesel dual-fuel premixed compression ignition engine. The effective CR was varied from 15.0 to 10.6 via the retardation of the intake valve closing timing (IVC) at 1,500 rpm. With respect to optimization, the diesel injection timing, fuel ratio, and exhaust gas recirculation (EGR) rate were adjusted for each optimized condition. The limitations were the maximum pressure rise rate (below 10 bar/deg) and in-cylinder pressure (below 150 bar) with NOx < 40 ppm and soot < 0.2 FSN. The results emphasized that when the effective CR was 12.7, the maximum load increased by 10.5 % (gIMEP from 13.3 to 14.7 bar) compared with that at a CR of 15.0. Although the decrease in CR resulted in a gross thermal efficiency loss, the difference was negligible (from 45.9 to 45.5 %). The main reason for high-load expansion was the increase in intake air volume under the same intake pressure upon lowering the CR and the margin for the maximum in-cylinder pressure. From this result, it can be concluded that the Miller cycle is useful for the expansion of high load ranges in premixed combustion systems. [ABSTRACT FROM AUTHOR]

In-cylinder flow motion is important for enhancing combustion in internal combustion engines. There are two major flow motions: tumble and swirl. Tumble enhances the flame propagation speed to spread throughout the entire cylinder. Swirl affects the behavior of diesel spray; an enhanced swirl ratio has been widely used in conventional diesel engines. Because dual-fueled combustion has the characteristics of premixed combustion from background fuels and mixing-controlled combustion from directly injected fuels such as diesel, understanding the effect of in-cylinder flow motion on combustion characteristics in dual-fuel combustion is critical. In this research, the effect of swirl in gasoline and diesel dual-fuel combustion was evaluated with different diesel injection timing conditions. As the dual-fuel combustion engine used in this research was driven by diesel spray, swirl was selected as the main flow motion rather than tumble. The effect of swirl with different diesel injection timings was investigated under low-speed and low-load conditions. The results demonstrate that increasing swirl intensity provokes fast-burning caused by the enhanced air-fuel mixture, decreasing the diesel fraction and allowing more exhaust gas recirculation (EGR) to be used for the reduction of engine-out nitrogen oxides (NOx) and smoke emissions, without reducing thermal efficiency. [ABSTRACT FROM AUTHOR]

The effects of intake pressures and EGR rates on the natural gas/diesel dual-fuel combustion under a high load condition (brake power of 100 kW) were evaluated using a 6-L CI engine in this study. Natural gas fraction was fixed as 80% of total input energy for all the dual-fuel combustion operations and engine rotation speed was set to 1,800 rpm. Intake pressure was varied from 0.15 to 0.21 MPa by controlling the waste gate type turbocharger system. EGR rate was changed mainly by controlling EGR valve opening from fully closing to mid-opening to fully opening, but it was also affected when intake pressures were varied. In addition to these intake mixture parameters, diesel injection timing was adjusted in two cases—early and late injections and all the experimental results were compared to those of the neat diesel combustion cases. The results emphasized that the dual-fuel combustion was more sensitive to overall equivalence ratio determined by intake pressures and EGR rates than the neat diesel combustion because it had flame propagation process of premixed natural gas and air mixture. Thus, during the dual-fuel operations, in-cylinder temperature and brake thermal efficiency were decreased as intake pressure was increased. [ABSTRACT FROM AUTHOR]

In this research, it was investigated the energy fraction and emission characteristics of natural gas/diesel dual-fuel combustion in terms of the combustion index such as combustion duration and mass fraction burned 50% (MFB50) of a 6-L heavy-duty compression ignition (CI) engine. The reactivity gradient was varied by changing the diesel injection timing and natural gas energy fraction from 60 to 90%. Engine speed was fixed at 1,200 rpm, and the total input energy from the two fuels was maintained at 11,880 J/cycle for all six cylinders. Diesel injection timing was varied from top dead center (TDC) to 40° before TDC (BTDC) (at intervals of 10°). First, the combustion parameters were analyzed in terms of differences in reactivity gradients. The main combustion parameters considered included ignition delay, combustion duration, and MFB 50. For all cases, the indicated thermal efficiency (ITE) was analyzed with respect to the energy fractions of combustion loss, heat transfer loss, and exhaust loss, to determine the main influences on combustion duration and the MFB 50. Engine-out emission was introduced as an operating parameter associated with ITE and the various losses. These values were compared to those of neat diesel combustion conditions. [ABSTRACT FROM AUTHOR]

This study investigated the effect of varying the spark advance timing and excess air ratio (air excessive ratio; λ) on the combustion and emission of nitrogen oxide (NOx) in a hydrogen-fueled spark ignition engine under part load conditions. The engine test speed was fixed at 2,000 rpm and the torque condition was 60 Nm. Excess air ratio was varied from the stoichiometric (λ = 1) to the lean mixture condition (λ = 2.2) by throttling. The spark advance timing was controlled to determine the maximum brake torque timing (MBT) for each excess air ratio value. Subsequent to the determination of the spark advance timing for MBT, the spark timing was varied from MBT timing to top dead center. Based on the results, it is concluded that the leanest mixture condition (λ = 2.2) with MBT spark timing exhibited the highest brake thermal efficiency of 34.17% and the NOx emissions were as low as 14 ppm. • Heat release from the residual gas follows the main combustion of hydrogen mixture at λ = 1. • Thermal efficiency increased up to 34% with pumping loss reduction at λ = 2.2. • Combustion loss does not exceed 0.32% and maximum unburned hydrogen occurred at λ = 1. • The lowest NOx emissions are 14 ppm and 0.07 g/kWh at λ = 2.2. [ABSTRACT FROM AUTHOR]

Abstract This study systematically investigated the application of a turbocharger system to a hydrogen spark ignition engine to extend operating limitations under high loads. The exhaust system of a commercial 2.4-L natural aspiration spark ignition engine was modified by adopting a turbocharger system. Engine test speeds were 2000–6000 rpm at intervals of 1000 rpm. The intake pressure was fixed for each experimental case, however, the quantity of hydrogen and spark advance timings were varied before the back-fire occurred. High load conditions under natural aspiration and turbocharging conditions were compared. The results indicated that distinctly higher boosts with the turbocharging system helped extend high load conditions, however, the high exhaust pressure obstructed the increasingly high load conditions under high speeds. Highlights • Power increased by up to 41% compared to N/A system with boosting at 2000 rpm. • Power decreased with boosting at 6000 rpm due to the deterioration of thermal efficiency. • Air-fuel mixture is leaner with boosting than with N/A at high engine speeds due to back-fire. • Higher pumping and friction losses with boosting resulted in lower power than those with N/A. [ABSTRACT FROM AUTHOR]

The diesel compression ignition (CI) engine has higher durability and thermal efficiency than the gasoline spark ignition (SI) engine. However, the high levels of nitrogen oxides (NOx) and particulate matter (PM) emissions are major problems of diesel engines due to the auto-ignition of heterogeneous mixtures. The dual-fuel combustion concept could be solution to environmental concerns. Dual-fuel combustion can be implemented by substituting some of the diesel fuel with high-volatility fuels, such as gasoline and natural gas. The premixed mixture condition can be improved to diminish localized rich and stoichiometric regions. Notably, ethanol has greater potential to reduce PM emissions because it is highly volatile and readily oxidized. For these reasons, in this research, the effects of varying the ethanol substitution ratio on engine performance and emissions under the dual-fuel combustion condition were experimentally investigated under various load conditions. The test engine was a heavy-duty single-cylinder diesel engine with two direct injectors. Engine speed was fixed at 1000 rpm and the load condition was varied for an indicated mean effective pressure (IMEP) ranging from 0.2 to 0.8 MPa. The ratio of ethanol to the total input energy was controlled from zero to nearly 50% of the input energy. The NOx and PM emissions decreased with increasing ethanol substitution and the mean size of the PM emissions decreased. For the mid-load condition (IMEP 0.6 MPa), the substitution was increased to 63%, but for low and high loads, higher ethanol fractions could not be used because of insufficient ignition energy at low loads and sharp increment of the in-cylinder pressure under high loads. [ABSTRACT FROM AUTHOR]

In this research, the effects of three operating parameters (Diesel injection timing, propane ratio, and exhaust gas recirculation (EGR) rates) in a diesel-propane dual fuel combustion were investigated. The characteristics of dual-fuel combustion were analyzed by engine parameters, such as emission levels (Nitrogen oxides (NO) and particulate matter (PM)), gross indicated thermal efficiency (GIE) and gross IMEP Coefficient of Variance (CoV). Based on the results, improving operating strategies of the four main operating points were conducted for dual-fuel PCCI combustion with restrictions on the emissions and the maximum pressure rise rate. The NOx emission was restricted to below 0.21 g/kWh in terms of the indicated specific NO (ISNO), PM was restricted to under 0.2 FSN, and the maximum pressure rise rate (MPRR) was restricted to 10 bar/deg. Dual-fuel PCI combustion can be available with low NO, PM emission and the maximum pressure rise rate in relatively low load condition. However, exceeding of PM and MPRR regulation was occurred in high load condition, therefore, design of optimal piston shape for early diesel injection and modification of hardware optimizing for dual-fuel combustion should be taken into consideration. [ABSTRACT FROM AUTHOR]

In this research, the effects of the propane ratio and diesel direct injection strategy on the emissions and combustion characteristics of a propane-diesel dual fuel PCCI (premixed charge compression ignition) engine were evaluated. Under low speed and low engine load, the propane ratio was varied from 30 to 70% to investigate the effect of the LHV (low heating value) fuel content in the supplied fuel (propane and diesel mixture). The EGR rate was adjusted to suit each propane ratio to ensure combustibility and restricted emissions. Early diesel injection strategies have an excellent effect on the dual fuel combustion in terms of simultaneously reducing NOx (nitrogen oxides) and PM (particulate matter) emissions. This concept is based on PCCI combustion, in which the ignition delay is longer than the diesel injection. Meanwhile, although early single diesel injection has been an effective strategy for reducing NOx and PM emissions simultaneously, it was possible to further reduce NOx emissions using an early split injection strategy with a 30% propane ratio. Additionally, when the propane ratio was 70%, the ignitibility deteriorated due to early single diesel injection, which led to a much leaner air–fuel mixture condition locally prior to auto-ignition, causing unstable combustion. As a result, a multiple injection strategy with earlier main injection and a small diesel post-injection as a triggering source was adopted to stabilize dual fuel PCCI combustion with a high propane ratio. The results emphasized that the diesel injection strategy could be adjusted to suit various propane ratios under dual fuel PCCI combustion to reduce NOx and PM emissions while maintaining thermal efficiency. [ABSTRACT FROM AUTHOR]

The key point of premixed compression ignition (PCI) combustion is an ignition delay time that is sufficient to premix the air and fuel. Thus, when PCI combustion is implemented with a single fuel, a very early start of injection (SOI) is usually applied, along with heavy exhaust gas recirculation. However, if two different fuels are used simultaneously for PCI combustion, it is possible to control the in-cylinder fuel reactivity by adjusting their ratio. Because an additional ignition delay control parameter is used for dual-fueled PCI combustion, its operating strategy and combustion characteristics differ from those of single-fueled PCI combustion. In this study, single-fueled and dual-fueled PCI combustions were compared using gasoline and diesel fuel under part-load conditions (1500 rpm and a low heating value of 580 J/str). In both cases, the diesel SOI was varied from the top dead center (TDC) to 35° BTDC to analyze the combustion characteristics. Under the optimized operating conditions, the target engine-out emissions were below the gross indicated specific NOx (gISNOx) of 0.4 g/kWh and gISsmoke of 20 mg/kWh. The results showed dual-fueled combustion is more suitable for PCI conditions than single-fueled combustion in terms of both the engine-out emissions and gross indicated thermal efficiency. • Combustion characteristics were compared between single-and dual-fueled. • Energy fraction analysis were verified under single-and dual-fueled. • Strategies for single- and dual-fueled premixed combustion were suggested. • Dual-fueled combustion was superior to single-fueled aspect of premixed combustion. [ABSTRACT FROM AUTHOR]

Hydrogen energy has received much attention in recent years due to its reliability and non-carbon products. However, it has been found that the backfire phenomenon plays a major part in limiting power and torque in the hydrogen internal combustion engine (H2ICE). Much research in recent years has considered turbocharger as a useful method to improve the power of H2ICE. Although the result of boosting a system with turbocharger became enhanced when compared to the natural aspiration system. Unfortunately, there were unsolved problems in exhaust backpressure and pumping losses that hindering the practical utilisation of H2ICE. This paper investigated the experiment of 2.4 L supercharged port fuel injection engine at 2000 rpm. Air excess ratio (lambda) was varied from stoichiometric to 2.8 by adjusting the boosting amount in supercharger, and throttling of the air. The hydrogen injection amount were maintained the same with turbocharger condition; spark advance timing was set at maximum brake torque. It was observed that by boosting engine with supercharger, the lower pumping loss and higher indicated mean pressure had been obtained when compared to turbocharger boosted engine under low-load condition. However, some additional power required for supercharging that lowers output of the engine. • Potential of using supercharger to increase the power output of a hydrogen engine. • Engine can be operated under very lean condition without abnormal combustion. • NOx emission of the supercharger engine was lower than the turbocharger one. • Hydrogen engine has the stable combustion ability even in very lean mixtures. [ABSTRACT FROM AUTHOR]

The port-injection-type hydrogen engine is advantaged in that hydrogen gas is injected into the intake pipe through a low-pressure fuel injector, and the mixing period with air is sufficient to produce uniform mixing, improving the thermal efficiency. A drawback is that the flame backfires in the intake manifold, reducing the engine output because the amount of intake air is reduced, owing to the large volume of hydrogen. Here, the backfire mechanism as a part of the development of full-load output capability is investigated, and a 2.4-liter reciprocating gasoline engine is modified to a hydrogen engine with a hydrogen supply system. To secure the stability and output performance of the hydrogen engine, the excess air ratio was controlled with a universal engine control unit. The torque, excess air ratio, hydrogen fuel, and intake air flow rate changes in time were compared under low- and high-engine speed conditions with a wide-open throttle. The excess air ratio depends on the change in the fuel amount when the throttle is completely opened, and excess air ratio increase leads to fuel/air-mixture dilution by the surplus air in the cylinder. As the engine speed increases, the maximum torque decreases because the excess air ratio continues to increase due to the occurrence of the backfire. The exhaust gas temperature also increases, except at an engine speed of 6000 rpm. Furthermore, the increase in exhaust gas temperature affects the backfire occurrence. At 2000 rpm, under low-speed and wide-open throttle conditions, backfire first occurs in the No. 4 cylinder because the mixture is heated by the relatively high port temperature. In contrast, at 6000 rpm, under high-speed and wide-open throttle conditions, the backfire starts at the No. 2 cylinder first because of a higher exhaust gas temperature, resulting in a lower excess air ratio in cylinders 2 and 3, located at the center of the engine. • The maximum torque decreases due to the backfire as the hydrogen engine speed increases. • The increase in the exhaust gas temperature affects the backfire with the increase in speed. • The backfire occurs in the No. 4 cylinder under low-speed conditions due to a higher port temperature. • The backfire starts in the cylinders located at the center of the engine under high-speed conditions. [ABSTRACT FROM AUTHOR]

• Effects of multi-angle injector on DF combustion was evaluated. • Multi-angle injector helped to reduce NMHC emissions under RCCI. • Multi-angle injector showed better GIE due to lower HT loss. • GWI could be improved more by multi-angle injector under RCCI. In this study, natural gas and diesel dual-fuel combustion in a heavy-duty compression ignition engine is experimentally evaluated by adopting a modified multi-angle nozzle of a diesel injector to reduce the global warming impact (GWI) factor while maintaining high thermal efficiency. The original injector has a single layer with an umbrella angle of 150° and eight holes, whereas the modified injector has an additional layer below with an injection angle of 90° and four holes. The engine speed is 1,200 rpm under low load conditions (intake pressure of 0.11 MPa and overall equivalence ratio of 0.5, such that the torque is varied); meanwhile, the natural gas fraction is varied from 45% to 71% while considering the combustion stability. The diesel injection timing is varied from the top dead center to 70° before top dead center at intervals of 10° for the injector nozzle conditions. Results show that the modified injector improves combustion efficiency under the reactivity-controlled compression ignition (RCCI) regime. In addition, the GWI factor is reduced by 5.6% compared with that of the original injector. Hence, RCCI combustion by early diesel injection using a multi-angle nozzle affords low emissions while considering the GWI factor, as well as maintains a high gross indicated thermal efficiency of 48.6%. [ABSTRACT FROM AUTHOR]

In this study, a hydrogen-fueled spark ignition engine was investigated for UAV operation, with a focus on its combustion region and idle condition. A 2.4l, four-cylinder spark ignition engine was used for experiments, with modification for hydrogen usage instead of gasoline. In experiments, the feasible combustion region and limitations of the combustion phenomena for the hydrogen-fueled spark ignition engine at specific load and speed conditions of 50 Nm and 2000 RPM were examined. It was found that owing to the wide flammability range of hydrogen, the air–fuel ratio could be varied from 1.0 to 2.4. However, misfire and backfire occurred because of the mixing issue and highly ignitable characteristics of the hydrogen–air mixture, respectively, under relatively rich conditions (excess air ratio between 1.0 and 1.5). Unstable combustion occurred under a relatively lean condition (excess air ratio>2.0). Considering important parameters such as the nitrogen oxide emissions, unburned hydrogen, and brake thermal efficiency, an excess air ratio between 1.8 and 2.0 with maximum brake torque timing (MBT) operation was appropriate for this condition. Extremely lean conditions with zero load can be achieved with stable combustion with the excess air ratio up to 3.0, which can almost eliminate nitrogen oxide emissions. • Unstable ignition causes misfire with advanced ignition timing at part load. • Backfire by undesirable ignition occurs with retarded ignition timing under λ > 1.6. • λ is limited to 1.8–2.0 at MBT due to NO x and unburned H 2. • NO x can be eliminated under stable idle operation. • Unburned H 2 is converted with commercial TWC of gasoline engine. [ABSTRACT FROM AUTHOR]

• Effects of fuel fractions and diesel SOI on THC are discussed. • Methane is related with crevice effect and bulk quenching. • NMHC is related with wall-wetting of diesel spray. • MFB50 position has strong influence on heat transfer loss. • RCCI improved the BTE with reduction of THC emissions. In dual-fuel combustion, the levels of total hydrocarbon (THC) emissions have increased, unlike the neat diesel compression ignition (CI) combustion. Intuitively, it can be inferred that most THC emissions are produced by the crevice effect of low-reactivity fuels (high-volatility fuels) under dual-fuel combustion. Additionally, it is possible that high levels of THC emissions are produced by dual-fuel combustion. If reactivity-controlled compression ignition (RCCI) combustion is applied by advancing the diesel injection timing to improve the premixing conditions, the occurrence of the wall-wetting effect may induce the production of high levels of THC emissions owing to incomplete combustion. Thus, in this study, the characteristics of non-methane hydrocarbons (NMHC) and methane emissions under general dual-fuel combustion conditions (diesel injection timings before top dead center (BTDC) 0 and 30 crank angle degree (CAD)) and RCCI conditions (diesel injection timings at 60 and 84 CAD BTDC) were investigated under a low-load in a 6-L heavy-duty engine. The natural gas fraction varied from 50% to the maximum level considering the combustion stability (coefficient of variance of indicated mean effective pressure). The results revealed that the overall THC emissions from the general dual-fuel combustion were higher compared with those of RCCI combustion, owing to the methane emissions from the squish area and the lower average in-cylinder temperature. Notably, methane emissions were dominant in the THC emissions (52–87%) under the general dual-fuel combustion condition, while NMHC emissions were a major part of the in THC emissions (61–87%) under the RCCI regimes. Hence, combustion inefficiency is a major concern in dual-fuel combustion. In this study, this problem was resolved by advancing the diesel injection timings. The findings in this study can be useful in the design of oxidation catalysts, regardless of whether the combustion regime is a general dual-fuel combustion or RCCI combustion considering the portion of methane emissions in the exhaust gas. Additionally, it is known that the RCCI combustion is superior to the general dual-fuel combustion with respect to higher thermal efficiency and low harmful THC emissions. [ABSTRACT FROM AUTHOR]