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Hydrogen engines show great potential as a power source with good combustion performance, zero carbon emissions, and diverse sources. However, the exhaust emission characteristics with high water vapor (H 2 O) content have not yet been clarified. This study presents the exhaust emissions of a heavy-duty direct-injection hydrogen engine under various operational parameters, with a focus on the H 2 O content. The results reveal important exhaust emissions characteristics of the hydrogen engine, including lower exhaust temperature (200 °C–400 °C), higher unburned H 2 emissions (up to 17100 ppm), less nitrogen oxide (NO) generation (<1000 ppm), and higher H 2 O content (6%–40%). Additionally, unburned H 2 rises, and NO and H 2 O decrease as the excess air ratio (λ) increases. When λ is greater than 3, NO levels fall sharply to below 100 ppm. Optimal emissions performance is achieved with a 5 °CA BTDC ignition timing where low levels of H 2 , H 2 O, and NO are maintained. Increasing hydrogen injection pressure decreases H 2 but raises exhaust temperature, H 2 O, and NO emissions. Excessively delaying hydrogen injection timing adversely affects the concentration gradient in the cylinder, increasing unburned H 2 emissions. The best emissions performance is observed at a hydrogen injection timing of 110 °CA BTDC. • Studied the exhaust emissions of heavy-duty direct-injection hydrogen engine. • Clarified the high H 2 O and H 2 emission characteristics of hydrogen engines. • Analyzed lower NO emissions and exhaust temperature from hydrogen engines. • Explored the effects of operating conditions on emission characteristics. [ABSTRACT FROM AUTHOR]

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To reduce knock and keeping low NOx emissions and high indicated thermal efficiency (ITE) in a hydrogen fuel engine, the comprehensive effects of ammonia substitution rate (ASR), compression ratio (CR), and ignition timing (IT) on its combustion and its NOx emissions were studied numerically. Based on a four‐cylinder gasoline direct injection (GDI) engine, it was modified into an ammonia/hydrogen dual‐fuel (AHDF) spark ignition (SI) engine. The simulation was conducted by GT‐Power software, and simulation data were validated through experiments. 2500 rpm_50% load was selected for the research. ASR, CR and IT vary from 0% to 20%, 10.5 to 8.5, and −24 to 0°CA ATDC, respectively. The findings indicate that increasing ASR decreases the maximum pressure rise rate (MPRR) and the knock index (KI), improving the ITE, but increasing NOx emissions. Based on 20% ASR, CR was optimized. The findings indicate that decreasing CR reduces the MPRR and KI, but increasing NOx emissions and decreasing the ITE. Finally, based on CR of 9, IT was optimized. The findings indicate that delaying IT reduces the MPRR and KI, but also has a certain impact on NOx emissions and ITE. After compromise consideration, the optimal IT in this study was selected as −9°CA ATDC. [ABSTRACT FROM AUTHOR]

Ammonia is a very promising alternative fuel for internal combustion engines, but there are some disadvantages, such as difficulty in ignition and slow combustion rate when ammonia is used alone. Aiming to address the problem of ammonia combustion difficulty, measures are proposed to improve ammonia combustion by blending hydrogen. A one-dimensional turbocharged ammonia-hydrogen engine simulation model was established, and the combustion model was corrected and verified. Using the verified one-dimensional model, the effects of different ratios of hydrogen to ammonia, different rotational speeds and loads on the combustion performance are investigated. The results show that the ignition delay and combustion duration is shortened with the increase of the hydrogen blending ratio. The appropriate amount of hydrogen blending can improve the brake's thermal efficiency. With the increase in engine speed, increasing the proportion of hydrogen blending is necessary to ensure reliable ignition. In conclusion, the ammonia-hydrogen fuel engine has good combustion performance, but it is necessary to choose the appropriate hydrogen blending ratio according to the engine's operating conditions and requirements. [ABSTRACT FROM AUTHOR]

Green hydrogen has become more attractive as a fuel for engines to reduce greenhouse gas emissions. By mixing it with natural gas (NG), the modification work on the engine can be minimized but the carbon dioxide emissions from combustion can still be decreased. In this paper, an experimental study was accomplished to investigate the performance of a spark-ignition engine fueled with hydrogen-natural gas blends by either keeping a constant ignition timing or changing it. Up to 25 mol-% hydrogen was mixed into natural gases with different compositions and the methane number and Wobbe index were calculated and compared to the requirements set by Euromot. The results show that up to 15 mol-% hydrogen can be blended into NG to meet the limits of Euromot. However, when 25 mol-% hydrogen was mixed into NG the methane number varied between 56 and 64 depending on the gas composition. This would most likely cause knock for a mixture consisting of higher hydrocarbons but during the executed tests knock was never a problem. Furthermore, it was detected that the methane number alone cannot tell the knock tendency of a gas in a certain engine and an additional condition is needed such as the hydrogen level. An adjusted ignition timing was also preferable compared to a constant one to keep the engine component temperature at a moderate level. • A SI-engine was fueled with different hydrogen-natural gas (H 2 -NG) mixtures. • Wobbe index and methane number (MN) were calculated for all test points. • Efficiency was improved and emissions were decreased with higher hydrogen content. • No tendency of knock when 25 mol-% hydrogen was mixed into natural gas with a low MN. • Additional condition is needed for MN eg. H 2 -level to be sure if knock can happen. [ABSTRACT FROM AUTHOR]

Efficient energy exploitation is a necessary issue because it helps reduce fuel consumption and environmental pollution. Finding the optimal ignition timing (IT) for diesel engines to create high power and efficiency deserves attention. This study utilizes AVL BOOST simulation software with the Vibe 2-Zone combustion model to investigate the effect of IT and combustion duration on engine characteristics such as power, torque, and brake-specific fuel consumption (BSFC) at different engine loads and speeds. Then, the prediction models of the optimal ITs versus combustion durations for maximum power and minimum BSPFC were computed. The results show that ITs strongly affect engine performance characteristics. The optimal ITs that the engine produces maximum power at different combustion durations are unaffected by engine load. In contrast, they are considerably influenced by engine load when considering the engine-generated BSFC. The correlations of optimal IT versus combustion duration are linear functions. The prediction models can be utilized to predict the optimal ignition timings of the engine since the experimental time can be reduced when applied to the actual engine.

This study presents an experimental investigation into the impact of blending bioethanol (E100) with conventional gasoline (E0), incrementally increasing biofuel levels up to E10, E50, and E70. The test was carried out in two stages: Stage I assessed the engine's performance under fixed speeds (n = 2000 rpm and n = 2500 rpm) and fixed throttle positions (15%, 20%, and 25%) to measure changes in engine torque, efficiency, and environmental metrics by varying the concentration of bioethanol in the fuel. Stage II aimed to enrich the initial findings by conducting an additional test, running the engine at a fixed speed (n = 2000 rpm) and braking torque (MB = 80 Nm) and varying the ignition timing. Results indicated slight improvements in engine brake torque and thermal efficiency (up to 1.7%) with bioethanol content increased to 70%, and a notable reduction in incomplete combustion byproducts—carbon monoxide and hydrocarbons emissions (up 15% and 43%). Nitrogen oxide emissions were reduced by up to 23%, but carbon dioxide emissions decreased by a mere 1.1%. In order to increase thermal efficiency by adding higher bioethanol blend concentrations, adjusting the ignition timing to counter the longer ignition delay is necessary; however, higher emissions of nitrogen oxides and hydrocarbons are a major drawback of such a strategy. The results of the research are important in determining the optimal concentration of bioethanol in the mixture with gasoline for the energy and environmental sustainability of a spark ignition engine. [ABSTRACT FROM AUTHOR]

Changing the ignition advance angle has a significant impact on the performance of a combustion engine. Optimization of ignition advance angle is a major task of adjusting the engine concerning emission standards, fuel consumption, torque value, etc. The results of the research showed that the process of optimizing the ignition advance curve can noticeably increase engine efficiency, as well as torque and power output from the engine while reducing fuel consumption as a result of lower indications of the air flow mass per second from MAF sensor (mass air flow sensor). The highest impact of the ignition advanced angle modifications can be seen in the area of the highest volumetric efficiency of the tested combustion engine. Almost no impact is observed within high engine speed levels. Simultaneously increasing engine load and rotation speed increases the possibility of engine knocking, which has a devastating effect on engine durability. [ABSTRACT FROM AUTHOR]

Background: Wildfires are thought to become more prevalent during periods of extended dry weather. This issue is examined using two dryness metrics commonly applied in Australian fire management agencies. Aims: This paper investigated links between wildfire incidence and the Keetch–Byram Drought Index (KBDI) and McArthur's Drought Factor (DF) across the state of Victoria, Australia. Methods: Weather records and data from 41 418 wildfires that occurred across the State over a 17-year period were compiled to examine the distributions of KBDI and DF on days with fires smaller and larger than 5 ha in area and all days, using kernel density plots. Key results: Days with fires, particularly days with fires that escaped initial attack, have higher DFs and KBDIs compared with all days. These differences vary between regions and are greatest in areas with moist climates. Conclusions and implications: An appreciation of dryness conditions using tools such as KBDI and DF is useful for understanding fire potential, particularly in areas that experience higher and more regular rainfall. McArthur's Drought Factor and the Keetch–Byram Drought Index are higher than normal on days with fires in Victoria, Australia. These metrics provide a more reliable indication of fire potential in high-rainfall areas than in lower-rainfall areas. This article belongs to the Collection Fire and Climate. [ABSTRACT FROM AUTHOR]

Ammonia is a very promising alternative fuel for internal combustion engines, but there are some disadvantages, such as difficulty in ignition and slow combustion rate when ammonia is used alone. Aiming to address the problem of ammonia combustion difficulty, measures are proposed to improve ammonia combustion by blending hydrogen. A one-dimensional turbocharged ammonia-hydrogen engine simulation model was established, and the combustion model was corrected and verified. Using the verified one-dimensional model, the effects of different ratios of hydrogen to ammonia, different rotational speeds and loads on the combustion performance are investigated. The results show that the ignition delay and combustion duration is shortened with the increase of the hydrogen blending ratio. The appropriate amount of hydrogen blending can improve the brake’s thermal efficiency. With the increase in engine speed, increasing the proportion of hydrogen blending is necessary to ensure reliable ignition. In conclusion, the ammonia-hydrogen fuel engine has good combustion performance, but it is necessary to choose the appropriate hydrogen blending ratio according to the engine’s operating conditions and requirements.

Hydrogen internal combustion engines (H2-ICEs) have advantages such as clean combustion and zero carbon emissions, and have become one of the important technical routes for decarbonization in the internal combustion engine industry. In this paper, several key factors affecting the performance and emissions of hydrogen internal combustion engines, such as ignition timing, excess air coefficient, and hydrogen injection timing, were systematically studied on a spark ignition multi-point injection (MPI) hydrogen internal combustion engine bench. The experimental results indicate that the ignition timing controls the combustion phase of hydrogen. Moderate early ignition can improve the brake thermal efficiency (BTE) while having little impact on the NOX emissions. Excess air coefficient(λ) can significantly affect the performance and emissions of H2-ICE. Along with the increase of the λ, the NOX emissions first increases and then continues to decline. When the λ reaching 2.1 or above, near zero emissions of NOX can be achieved. The advance of hydrogen injection timing will slightly increase the peak of cylinder pressure and instantaneous heat release rate. However, overall, the impact of hydrogen injection timing on BTE and NOX emissions is not significant on MPI H2-ICE.

An innovative analytical approach combining game theory and particle swarm algorithms is used for the performance optimisation problem of hydrogen engines.An innovative analysis method combining game theory and particle swarm optimization algorithm was adopted to optimize the performance of hydrogen engines. Firstly, the power performance, fuel economy and emission of hydrogen internal combustion engines are studied in detail, and a three-way game model is constructed with the three as the main players, with strategic attribution for ignition timing, hydrogen injection timing and compression ratio.The simulation process of the model is then transformed into numerical optimisation by integrating the game utility function. Finally, the particle swarm algorithm is used to determine the initial set of strategies to obtain the Nash equilibrium solution.The results of the study showed that the optimized hydrogen internal combustion engine improved its power performance by 3.6%; economic efficiency increased by 5.7%; and emissions were reduced by 2% compared to the original engine. • Transforming the optimisation problem of the H2-ICE into a game theoretic problem. • A multi-objective optimization strategy based on game theory is proposed. • Determine the initial set of strategies and find the Nash equilibrium solution using particle swarm algorithm. • The operating parameters of the H2-ICE at variable compression ratios were optimally designed. [ABSTRACT FROM AUTHOR]

This study presents a new knock control criterion based on different loads and engine power output loss. By utilizing a modified port fuel injection (PFI) spark-ignition (SI) methanol marine engine, the suppressive effects of retarding ignition timing, reducing air-fuel ratio and delaying injection timing on knock intensity at different loads were investigated. Subsequently, a comparative analysis of three knock control strategies was conducted to determine their impacts on power output and thermal efficiency, thus proposing the optimal knock control strategy at different loads. The results show that at both low load (MAP = 73 kPa) and high load (MAP = 139 kPa), the high knock intensity in KLSA (knock-limited spark advance) +5 case is reduced to the safety limitation by retarding ignition timing and reducing air-fuel ratio, while retarding injection timing can effectively suppress knock only at low load. Furthermore, under KLSA+5 condition, there is a significant increase in the probability of severe knock for CA05 earlier than the knock boundary. As the knock tendency is mitigated, IMEP reduces monotonically. There is lower power output loss by optimizing injection timing and air-fuel ratio at low load, and optimizing ignition timing at high load, while the air dilution strategy consistently results in minimal thermal efficiency loss. • The effects of ignition timing, air dilution, and injection strategy on knock suppression are investigated. • The comparative analysis of combustion characteristic under three control strategies is conducted. • Delaying injection timing and decreasing air-fuel ratio at low load obtain the smaller power loss under knock limit. • For high load, retarding ignition timing can maintain minimal power loss within knock limitation. • A new knock control criterion is proposed. [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]

Hydrogen/natural gas blends fuel is considered one of the ideal alternative fuels for improving the thermal efficiency and reducing carbon emissions of rotary engine. In order to further enhance the combustion and power performance of rotary engine, a new method of the setting of bluff bodies in the cylinder was proposed. The influence of bluff-body settings in the cylinder on the combustion, power performance, and NO generation was numerically studied under different ignition timings. The results indicated that in-cylinder bluff-body settings could influence flame propagation by affecting the turbulent kinetic energy and mixture distribution during the process from the late compression stroke to the combustion stroke. Further, for any fixed bluff-body shape in the cylinder, there is a trade-off relationship between the non-blockage ratio and squish velocity at the cylinder block center section as the ignition timing is progressively advanced or delayed. Consequently, considering the above trade-off relationship, the triangular slotted bluff-body in combination with an ignition timing of 30° CA (BTDC) could be used to achieve the maximum improvement in the combustion and power performance of rotary engine. The peak pressure exhibited a growth of 4.83%, and the indicated mean effective pressure increased by 1.46%. • Using hydrogen/natural gas blend fuel to reduce carbon emissions from the rotary engine. • A novel in-cylinder bluff-body structure in the rotary engine is proposed. • Systematic study of in-cylinder bluff-body effects on the combustion process. • A trade-off relationship influenced by the bluff body is identified. • The optimal structure of the bluff-body is provided for improving performance. [ABSTRACT FROM AUTHOR]

The Miller cycle has significant advantages of suppressing knocking and improving nitrogen oxide (NO X) emissions without the penalties of reducing engine fuel consumption and power output. In the study, the effect of non-Miller cycle and Miller cycle on the exhaust gas recirculation (EGR) introduction capability and the knocking boundary were evaluated on a stoichiometric combustion natural gas engine at three different loads. Additionally, the effect of Miller cycle coupled EGR and ignition timing on engine performance and combustion process was discussed. The results indicate that, for the same condition, the Miller cycle could reduce peak temperature and pressure, increased combustion duration, and delayed combustion phase, which makes for effective knocking suppression. Therefore, the Miller cycle has less dependence on the EGR strategy to control knock. Moreover, the Miller cycle can also reduce the ability to introduce EGR, which could up to 3.8%. By matching the ignition timing and EGR rate, the BSFC of the Miller cycle were decreased by 0.6g/kW·h, 2.4 g/kW·h and 2.9 g/kW·h respectively for three test conditions compared with non-Miller cycle. In terms of emissions, the Miller cycle and EGR can both suppress NO X emissions, while the EGR being more effective. The study will provide valid information for the application of the Miller cycle to achieve efficiency clean combustion of natural gas engine. • The effect of different cycles on the boundary parameters of the engine is compared. • The effect of the Miller cycle on the combustion process of the engine is investigated. • The potential for optimizing fuel economy and improving NO X emissions of Miller cycle coupled EGR is explored. [ABSTRACT FROM AUTHOR]

Influences of ignition timing (IT) on combustion, carbon monoxide (CO) and nitric oxide (NO) regulated emissions and formaldehyde (HCHO) and unburned methanol (CH 3 OH) unregulated emissions in a hydrogen (H 2)/methanol dual-injection automobile engine under lean-burn condition were studied numerically. The results demonstrate that at lean-burn (excess air ratio = 2.0) condition, the peak cylinder pressure (PCP), peak heat release rate (PHRR) and peak cylinder temperature (PCT) all decrease with delayed IT, and their corresponding crank angles are also late; ignition delay (ID) and combustion duration (CD) decrease with delayed IT; CO, HCHO and CH 3 OH emissions increase with delayed IT, while NO emission decreases with delayed IT. At a fixed IT, PCP, PHRR and PCT for with adding 5 % H 2 (R H2 = 5 %) are higher than those for without adding H 2 (R H2 = 0 %), and their corresponding crank angles for R H2 = 5 % are earlier than those for R H2 = 0 %; ID and CD for R H2 = 5 % are lower than those for R H2 = 0 %. CO, HCHO and unburned CH 3 OH emissions for R H2 = 5 % are also much lower than those for R H2 = 0 %, while NO emission for R H2 = 5 % is also higher than that for R H2 = 0 %. The influence order of adding H 2 to reduce emissions of engine is: CO > HCHO > unburned CH 3 OH. • H 2 /methanol dual-injection was proposed to improve HCHO and unburned CH 3 OH emissions. • The role of H 2 -assisted combustion was revealed. • Influence of increasing H 2 on promoting combustion is obvious. • Influence order of adding H 2 to reduce emissions is: CO > HCHO > unburned CH 3 OH. [ABSTRACT FROM AUTHOR]

• The separate effects of water injection timing, injection pressure and ignition timing on engine performance are researched. • Ignition advance eliminates combustion deterioration caused by port water injection. • The combined influence mechanism of the control parameters is studied based on the Taguchi method. • The optimal parameter combination of the combustion characteristic and the lowest emission is obtained. • Injection timing affects engine performance more than injection pressure. For the engine with port water injection, the control parameters including injection timing, injection pressure and ignition timing are critical to balance engine performance. To maximize the advantages of water injection, a series of experiments and simulations were conducted to investigate the separate effects of the control parameters on the combustion and emission. Then, the Taguchi method with an L16 orthogonal array was used to study the combined effects of the control parameters. In addition, the engine performance was considered to evaluate the influence degree of the control parameters using the signal-to-noise ratio and the analysis of variance. The result showed that injection timing and injection pressure played an important role in the spark ignition engine. The three-body effect outweighed the thermal effect with the delay of water injection timing, which accelerated the combustion progress and increased the NOx emission. Secondly, ignition advance eliminated combustion deterioration caused by port water injection. Thirdly, the combination of the control parameter of the optimum combustion characteristic and the lowest emission was acquired. The optimum combustion characteristic was acquired at 310 °CA injection timing, 5.0 MPa injection pressure and 44 °CA ignition timing. The lowest emission was acquired at 350 °CA injection timing, 10.6 MPa injection pressure, and 44 °CA ignition timing. Injection timing affects the combustion and emission more than injection pressure. [ABSTRACT FROM AUTHOR]