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This study investigates the effect of hydrogen enrichment in a direct-injected methanol-fuelled SI engine, with combustion and emission performance analysed by varying the methanol injection timing from 150° to 60° CA bTDC. A three-dimensional computational fluid dynamic model of the hydrogen-enriched methanol engine was developed to predict the engine performance, in-cylinder, and emission characteristics. The numerical model was solved using three-dimensional Reynolds-Averaged Navier Stokes, the RNG k-epsilon model for turbulence, the O'Rourke and Amsden sub-model for heat transfer, the extended Zeldovich mechanism for nitric oxide emissions, and the Hiroyasu-NSC model for soot emissions. The results indicated that retarding the injection timing resulted in a decrease in the indicated specific CO and soot emissions along with a rise in the indicated specific NOx emissions. Furthermore, hydrogen enrichment with methanol enhanced the hydroxyl radical concentration, reduced the combustion duration, reduced also the indicated specific CO and soot emissions while increasing the indicated specific NOx emissions. The study indicates that hydrogen enrichment could extend the late injection timing limit of methanol by enhancing fuel-air mixing, which improves and controls the combustion process more effectively. • Hydrogen enrichment extended the late injection limit of methanol. • Injection timing improved fuel-air mixing and controlled combustion process. • Methanol performance was limited for high hydrogen additions. • Hydrogen addition to methanol enhanced mixing and combustion. [ABSTRACT FROM AUTHOR]

In the endeavor to accomplish a fully de-carbonized globe, sparkling interest is growing towards using natural gas (NG) having as vastly major component methane (CH4). This has the lowest carbon/hydrogen atom ratio compared to other conventional fossil fuels used in engines and power-plants hence mitigating carbon dioxide (CO2) emissions. Given that using neat hydrogen (H2) containing nil carbon still possesses several issues, blending CH4 with H2 constitutes a stepping-stone towards the ultimate goal of zero producing CO2. In this context, the current work investigates the exergy terms development in high-speed spark-ignition engine (SI) fueled with various hydrogen/methane blends from neat CH4 to 50% vol. fraction H2, at equivalence ratios (EQR) from stoichiometric into the lean region. Experimental data available for that engine were used for validation from the first-law (energy) perspective plus emissions and cycle-by-cycle variations (CCV), using in-house, comprehensive, two-zone (unburned and burned), quasi-dimensional turbulent combustion model tracking tightly the flame-front pathway, developed and reported recently by authors. The latter is expanded to comprise exergy terms accompanying the energy outcomes, affording extra valuable information on judicious energy usage. The development in each zone, over the engine cycle, of various exergy terms accounting too for the reactive and diffusion components making up the chemical exergy is calculated and assessed. The correct calculation of species and temperature histories inside the burned zone subsequent to entrainment of fresh mixture from the unburned zone contributes to more exact computation, especially considering the H2 percentage in the fuel blend modifying temperature-levels, which is key factor when the irreversibility is calculated from a balance comprising all rest exergy terms. Illustrative diagrams of the exergy terms in every zone and whole charge reveal the influence of H2 and EQR values on exergy terms, furnishing thorough information. Concerning the joint content of both zones normalized exergy values over the engine cycle, the heat loss transfer exergy curves acquire higher values the higher the H2 or EQR, the work transfer exergy curves acquire slightly higher values the higher the H2 and slightly higher values the lower the EQR, and the irreversibility curves acquire lower values the higher the H2 or EQR. This exergy approach can offer new reflection for the prospective research to advancing engines performance along judicious use of fully friendly ecological fuel as H2. This extended and in-depth exergy analysis on the use of hydrogen in engines has not appeared in the literature. It can lead to undertaking corrective actions for the irreversibility, exergy losses, and chemical exergy, eventually increasing the knowledge of the SI engines science and technology for building smarter control devices when fueling the IC engines with H2 fuel, which can prove to be game changer to attaining a clean energy environment transition. [ABSTRACT FROM AUTHOR]

This study investigated the performance, emission reactions, and combustion of liquefied petroleum gas (LPG) at various volumetric ratios with gasoline. The experiments were carried out on a single cylinder spark ignition (SI) engine at different engine loads (500 to 3000 W). In general, the use of LPG has a negative effect on performance and combustion, while making a positive contribution to emissions. The brake thermal efficiency (BTE) and brake specific fuel consumption (BSFC) values closest to 100% gasoline were obtained with 25% LPG and were lower by 0.36% and 4.55%, respectively. Conversely, using LPG resulted in lower emissions of carbon dioxide (CO2), hydrocarbons (HC), and carbon monoxide (CO). The lowest emissions were obtained with the use of 100% LPG as 0.5%, 65 ppm and 9.5%, respectively. Compared to 100% gasoline, 20.63%, 27.78% and 5.19% improvements were achieved. Finally, the cylinder gas pressure value was negatively affected using LPG. Compared to 100% gasoline, the gas pressure value obtained with 75% LPG content fuel was 7.81% lower. It has been concluded that LPG is an environmentally friendly alternative fuel in terms of emissions, and considering the decrease in performance values, 25% LPG can be used successfully in SI engines instead of 100% LPG. [ABSTRACT FROM AUTHOR]

An experimental investigation on the spatial distribution of knock events in a turbocharged spark-ignition engine for hybrid vehicle applications was conducted by using a multichannel fiber optic method. The knock positions were detected under different conditions to investigate the influence of crucial engine design and operating parameters on the knock characteristics including the spatial distribution in the combustion chamber and its relationship to knock intensity. The measured data reveal that the spatial distribution in the engine with a port fuel injection (PFI) system is mainly located on the exhaust side with insignificant influence of engine speed and load, which is attributed to the elevated thermal load around the exhaust valves. However, the knock events under gasoline direct-injection (DI) conditions were found to occur in more scattered locations with more occurring on the engine front-end and rear-end sides. These results indicate that the in-cylinder fuel-air mixing process may have a significant impact on the knock occurrence spots under DI conditions. The knock positions of the engine with different excessive air ratios, injection timings, and intake-valve timings were also detected, indicating that engine operating parameters have complex influences on the knock-region distribution in a DI engine. In addition, experiments were also carried out in two different cylinders to verify the cylinder-to-cylinder variations in knock regions which may be caused by the engine cooling design. Furthermore, no apparent correlations were observed between the knock position and the knock intensity by analysis of the experimental data. [ABSTRACT FROM AUTHOR]

In this study, the performance and exhaust emissions of a spark-ignition (SI) engine were simulated using AVL program, and the outcomes were compared with the results coming from experiments. The simulated engine was operated at a constant speed (1600 rpm) and various engine powers with gasoline (G100), and it blends with different higher-order alcohols such as 1-hexanol (HEX) and 1-heptanol (HP) as new fuel combinations. The proportions of tests fuel combinations were G100, G100 + HEX (5, 10, 15, and 20%) and G100 + HP (5, 10, 15, and 20%). The experimental study showed that the highest brake-specific fuel consumption was calculated to be 0.625 kg/kWh using HP20 fuel at 1 kW of engine power, while it was found to be 0.598 kg/kWh in the numerical study. The experimental research indicated that the lowest CO emission was emitted to be 0.28% in HEX20 fuel at 5 kW of engine power. Under the same condition, it was found 0.26% in the simulation study. The highest NOx emission was measured to be 1349.8 ppm in HEX20 fuel at 5 kW of the engine power. Meanwhile, 1318.3 ppm was found in the simulation. When the simulation outcomes were compared with the experimental study results, the simulation results were in valid. The difference in brake-specific fuel consumption results between experimental and numerical research ascended as the engine power jumped up. Furthermore, reductions were observed in the amount of difference in the results related to emissions between experimental and simulation studies at higher engine powers. [ABSTRACT FROM AUTHOR]

New generations of spark-ignition engines include exhaust gas recirculation (EGR) to improve the engine efficiency. Depending on the design of the EGR routing, some differences in the total amount of recirculated gases that reach each cylinder can be induced. This affects the air-to-fuel ratio on each cylinder due to the combination of the different temperature and composition of the gases at the intake valve closure. As a consequence, significant deviations in the combustion process and the subsequent composition upstream the three-way catalyst can be reached. This paper explores these effects on catalyst performance and tailpipe emissions, individualizing the behavior for each regulated species. The study was performed in a four-cylinder naturally aspirated engine with Atkinson cycle and a close-coupled three-way catalyst. The most significant deterioration in conversion efficiency appeared for the nitrogen oxides, directly linked to the EGR dispersion level. In the case of carbon monoxide (CO) emissions, no significant impact was observed except at high average EGR rates, where one or more of the cylinders exceeded the EGR tolerance for that speed and load. Based on these results, a strategy where the fuel injector command is adapted to correct the air-to-fuel ratio deviations induced by the EGR was developed and implemented. [ABSTRACT FROM AUTHOR]

A novel concept to suppress knock combustion using the targeted fuel injection in a spark-ignition (SI) engine is proposed, which utilizes a customized injector to inject a small portion of the total fuel toward the end-gas region in the late compression stroke so that charge cooling effect by fuel vaporization is imposed on the local mixtures. CFD studies were carried out to evaluate the effects of various targeted fuel injection strategies on the processes of charge cooling, air-fuel mixing and combustion in a 1.2-L gasoline SI engine with a high compression ratio. A knock prediction model adopting a level set G-equation model coupled with a transported Livengood-Wu integral correlation was applied to predict the knock event by capturing the occurrence of end-gas auto-ignition. It was found that the local gas temperatures in the sprayed region decreased and knock combustion tendency was suppressed indeed, and the degree of the reduction in local gas temperature and knock tendency was affected by the selected targeted injection strategy. However, the results also indicated that excessive fuels injected could result in worsen air-fuel mixing that led to incomplete combustion. Hence, the injection strategy needs to be optimized by balancing the knock tendency and combustion efficiency. The study further shown that the spark timing could be advanced by 3.3° crank angle in a particular injection strategy case by comparing with the non-targeted-injection case, which demonstrated the effectiveness of the proposed concept. [ABSTRACT FROM AUTHOR]

An optically accessible single-cylinder spark-ignition engine operated under homogeneous, part-load conditions is experimentally investigated using optical and spark diagnostics to evaluate the relationship between the spark, flow, and flame with increasing dilution using several levels of exhaust gas recirculation (EGR). Voltage and current measurements of the secondary spark circuit are compared with simultaneous high-speed spark plasma imaging, particle image velocimetry measurements of the flow field, and burned gas images. Specifically, characteristic restrike cycles and normal cycles are examined under the 0 % EGR and 12.9 % EGR conditions to reveal a relationship between the magnitude and direction of the velocity near the spark plug and the spark's behavior coupled with that of the subsequent flame propagation. Through the use of conditional statistics and correlation analysis of data sets of all non-restrike and all restrike cycles, the horizontal velocity across the spark gap was identified as a critical quantity in facilitating more stable and faster combustion under diluted mixture conditions. [ABSTRACT FROM AUTHOR]

In the endeavor to accomplish a fully de-carbonized globe, sparkling interest is growing towards using natural gas (NG) having as vastly major component methane (CH4). This has the lowest carbon/hydrogen atom ratio compared to other conventional fossil fuels used in engines and power-plants hence mitigating carbon dioxide (CO2) emissions. Given that using neat hydrogen (H2) containing nil carbon still possesses several issues, blending CH4 with H2 constitutes a stepping-stone towards the ultimate goal of zero producing CO2. In this context, the current work investigates the exergy terms development in high-speed spark-ignition engine (SI) fueled with various hydrogen/methane blends from neat CH4 to 50% vol. fraction H2, at equivalence ratios (EQR) from stoichiometric into the lean region. Experimental data available for that engine were used for validation from the first-law (energy) perspective plus emissions and cycle-by-cycle variations (CCV), using in-house, comprehensive, two-zone (unburned and burned), quasi-dimensional turbulent combustion model tracking tightly the flame-front pathway, developed and reported recently by authors. The latter is expanded to comprise exergy terms accompanying the energy outcomes, affording extra valuable information on judicious energy usage. The development in each zone, over the engine cycle, of various exergy terms accounting too for the reactive and diffusion components making up the chemical exergy is calculated and assessed. The correct calculation of species and temperature histories inside the burned zone subsequent to entrainment of fresh mixture from the unburned zone contributes to more exact computation, especially considering the H2 percentage in the fuel blend modifying temperature-levels, which is key factor when the irreversibility is calculated from a balance comprising all rest exergy terms. Illustrative diagrams of the exergy terms in every zone and whole charge reveal the influence of H2 and EQR values on exergy terms, furnishing thorough information. Concerning the joint content of both zones normalized exergy values over the engine cycle, the heat loss transfer exergy curves acquire higher values the higher the H2 or EQR, the work transfer exergy curves acquire slightly higher values the higher the H2 and slightly higher values the lower the EQR, and the irreversibility curves acquire lower values the higher the H2 or EQR. This exergy approach can offer new reflection for the prospective research to advancing engines performance along judicious use of fully friendly ecological fuel as H2. This extended and in-depth exergy analysis on the use of hydrogen in engines has not appeared in the literature. It can lead to undertaking corrective actions for the irreversibility, exergy losses, and chemical exergy, eventually increasing the knowledge of the SI engines science and technology for building smarter control devices when fueling the IC engines with H2 fuel, which can prove to be game changer to attaining a clean energy environment transition.

Hydrogen combustion engines are considered one of the leading solutions for decarbonizing road transport, mainly due to the possibility of adapting current engines for hydrogen operation with minor changes. This research extensively analyzes the effect of combined EGR (exhaust gas recirculation) and VVT (variable valve timing) strategies on the performance and emissions of a commercial turbocharged SI engine fueled with hydrogen. To this end, a 1D model of the said engine, widely validated for gasoline operation, was adapted to simulate the engine's behavior with hydrogen. This adaptation involved hardware changes and the implementation of a predictive hydrogen combustion submodel, previously calibrated using experimental data from a single-cylinder engine of similar geometry. Firstly, 400 hydrogen engine simulations without EGR were conducted to optimize the VVT system for fuel efficiency over a wide operating range. A detailed explanation of the causality of varying valve overlap on pumping losses, in-cylinder gas composition, and combustion is provided from these simulations. Then, a series of EGR sweeps were simulated to study its impact on performance and NOx at various degrees of load; concluding that diluting with EGR, rather than air, leads to reduced NOx emissions in exchange for slightly increased fuel consumption. • Adaptation of a Euro 6 turbocharged DI SI engine for hydrogen operation • Deep analysis of the VVT and EGR impact on thermal efficiency and emissions • EGR dilution is more effective in reducing NO X but penalizes fuel consumption • EGR leads to a low-end torque increase of 5–16% at iso-NO X conditions [ABSTRACT FROM AUTHOR]

Reynolds-Averaged Navier–Stokes (RANS) simulations of a spark-ignition engine are performed to examine different modes of hydrogen combustion under a large range of conditions. Twelve cases featuring different spark timings, equivalence ratios, and compression ratios are simulated. A consistent methodology is used across all cases without any adjustment to the turbulent flame speed model constant. A rigorous validation against the experimental data is also undertaken. The simulations capture four distinct combustion modes: normal, knocking, superknock or detonation and fast flame propagation. Specifically, for the fast flame propagation mode, a relatively fast spark-ignited flame is observed at lower compression ratios under stoichiometric conditions, resulting in large pressure fluctuations within the engine. It is also shown that the competition between flame timescale and ignition delay plays a crucial role in characterising the combustion mode under various conditions. • Hydrogen combustion in a CFR engine is simulated using RANS under a large range of operating conditions. • The simulation results are validated using the in-cylinder experimental pressure trace for all cases with consistent numerical settings. • Normal and knocking combustion, fast flame propagation, and detonation are all well captured in the simulations. • Fast propagation of hydrogen flame can cause large pressure oscillations without featuring end-gas auto-ignition. • Different combustion modes can be effectively characterised using both the premixed flame timescale and the ignition delay time of the end-gas. [ABSTRACT FROM AUTHOR]

This present study showed a comprehensive analysis of energy, exergy, performance, and emission characteristics of a spark-ignition engine powered by blends of gasoline-isoamyl alcohol-ethanol at volume proportions (100_0_0)% (P0E0), (90_5_5)% (P5E5), (80_5_15)% (P5E15), and (70_5_25)% (P5E25) at various engine speeds and compression ratios (CR). The outcomes of thermodynamic analyses revealed that the highest exergy and energy efficiency were 28.92 % (P0E0, 2600 rpm, CR of 9:1) and 31.01 % (P0E0, 2600 rpm, CR of 9:1), respectively. In addition, the average brake power and brake thermal efficiency for P0E0, P5E5, P5E15, and P5E25 increased by (30.36 %, 27 %, 26.74 %, 27.84 %) and (0.34 %, 0.07 %, 0.35 %, 0.33 %) respectively, while brake specific fuel consumption decreased by (2.5 %, 0.64 %, 3.62 %, 6.33 %) in the engine speed range of 2600–3200 rpm. Compared to gasoline, the maximum reduction of carbon monoxide emissions was 6.13 %, 8.81 %, and 9.96 %, while unburnt hydrocarbon emissions exhibited the maximum decrement by 5.8 %, 10.75 %, 12.58 % for P5E5, P5E15, and P5E25, respectively. However, nitrogen oxide (NOx) emissions for P5E25 tended to increase significantly compared to P0E0, while the difference in NOx emissions for P5E15 and P0E0 was marginal. Overall, P5E15 could be considered as the potential alternative fuel for spark-ignition engines towards the goal of sustainable energy conversion. [Display omitted] • Gasoline and ethanol blends with 5 % of isoamyl alcohol were used for all tests. • Energy, exergy, performance, and emission analysis were conducted in an SI engine. • The highest exergy and energy efficiency for blends exhibited at 3000 rpm. • Addition of ethanol and isoamyl alcohol to gasoline lowered pollutant emissions. [ABSTRACT FROM AUTHOR]

In the automotive sector, hydrogen is being increasingly explored as an alternative fuel to replace conventional carbon-based fuels. Its combustion characteristics make it well-suited for adaptation to internal combustion engines. The wide flammability range of hydrogen allows for higher dilution conditions, resulting in enhanced combustion efficiency. When combined with lean combustion strategies, hydrogen significantly reduces environmental impact, virtually eliminating carbon dioxide and nitrogen oxide emissions while maintaining high thermal efficiency. This paper aims to assess the potential of using an outwardly opening poppet valve hydrogen direct injection (DI) system in a small engine for light-duty applications. To achieve this, a comparison of performance, emission levels, and combustion parameters is conducted on a single-cylinder spark-ignition (SI) research engine fueled by hydrogen, using both port fuel injection (PFI) and this new direct injection system. Two different engine loads are measured at multiple air dilution and injection timing conditions. The results demonstrate notable efficiency improvements, ranging from 0.6% to 1.1% when transitioning from PFI to DI. Accurate control of injection timing is essential for achieving optimal performance and low emissions. Delaying the start of injection results in a 7.6% reduction in compression work at low load and a 3.9% reduction at high load. This results in a 3.1-3.2% improvement in ISFC in both load conditions considered. • A novel hydrogen medium-pressure direct injection system has been evaluated. • Direct injection improves gross indicated efficiency levels between 0.6%–1.1%. • ISFC gains around 3% are achieved with delayed SoI using a direct injection system. • Nitrogen oxide levels are minimized by combining dilution and injection strategies. • Results hint that controlling stratification may enhance efficiency and pollutants. [ABSTRACT FROM AUTHOR]

The impacts of excess air ratio (λ) on combustion, CO and NO regulated emissions, and formaldehyde (HCHO) and unburned methanol (CH 3 OH) unregulated emissions behaviors in a spark-ignition H 2 /methanol dual injection engine were studied numerically. The results show that the peak in-cylinder pressure (PIP), peak heat release rate (PHRR) and peak in-cylinder temperature (PIT) all decrease with the increase of λ , and their corresponding crank angles are also late; the ignition delay (ID) and combustion duration (CD) decrease with the increase of λ ; the CO, HCHO and CH 3 OH emissions increase with the increase of λ , while the NO emission decreases with the increase of λ. At a constant λ , the PIP, PHRR and PIT for with 5 % H 2 (R H2 = 5 %) are higher than those for without H 2 (R H2 = 0 %), and their corresponding crank angles for R H2 = 5 % are earlier than those for R H2 = 0 %; the ID and CD for R H2 = 5 % are lower than those for R H2 = 0 %. The CO, HCHO and CH 3 OH emissions for R H2 = 5 % are also much lower than those for R H2 = 0 %, while the NO emission for R H2 = 5 % is also higher than that for R H2 = 0 %. The impact order of adding H 2 to reduce emissions of H 2 /methanol dual-injection engine is: CO ≥ HCHO > unburned CH 3 OH. • H 2 -assisted combustion was proposed to improve the combustion and emissions of H 2 /methanol engine.. • The role of H 2 -assisted combustion was revealed.. • Adding H 2 is more beneficial to improve the firing characteristics under lean burn. • The impact order of adding H 2 to reduce emissions is: CO ≥ HCHO > unburned CH 3 OH. [ABSTRACT FROM AUTHOR]

This paper assesses the cyclic variability (cycle-by-cycle variations (CCV)) of combustion, performance and nitric oxide (NO) emissions in high-speed (HS), spark-ignition (SI) engine fueled with hydrogen-enriched methane (CH 4), for which experimental data are available. Thus, in-house, two-zone, quasi-dimensional turbulent combustion model is used that closely trails the flame-front movement, which was validated before regarding performance, emissions, exergy, and CCV for gasoline- or methane-run HSSI engines. It is enhanced herein to study CCV of performance, combustion, and NO emissions, with engine fueled by various hydrogen-methane blends (up to 50 % by vol. hydrogen) and equivalence ratios (EQR). Hence, the influence of flame-kernel turbulence and EQR variation mechanisms on CCV attributes is considered and assessed. The numerical results are compared with measured data of cylinder pressure, indicated mean effective pressure (IMEP), and NO emissions at 'steady' conditions, and further for validation against available experimental CCV results for IMEP at all operating conditions. That CCV analysis is extended to peak pressure, IMEP, and NO emissions using coefficients of variation (COV), frequency distributions, and pertinent diagrams illuminating their cycle-by-cycle variations. The CCV variations decrease with hydrogen content in the blend whereas they increase with the mixture leanness delineating the relative merits of the two mechanisms. • CCV study in SI engine run on H 2 /CH 4 blends with in-house, quasi-dimensional model. • Influence on CCV of flame-kernel turbulence and fuel-air ratio variation mechanisms. • The two mechanisms impact differently on various performance and emission parameters. • CCV evaluation of peak pressure, IMEP, combustion attributes, and NO emission. • CCV variations decrease with hydrogen content in the blend and mixture richness. [ABSTRACT FROM AUTHOR]