Combustion Characteristics Of Engine Research Articles

Improvement of Engine Combustion and Emission Characteristics by Fuel Property Modulation

The sustainability of diesel engines has come to the forefront of research with the growing global interest in reducing greenhouse gas emissions and improving energy efficiency. The aim of this paper is to support the goal of sustainable development by improving the volatile properties of diesel fuel to promote cleaner combustion in engines. In order to study the effect of diesel fuel volatility on spraying, combustion, and emission, the tests were carried out with the help of the constant volume chamber (CVC) test rig and an engine test rig, respectively. CVC test: A high-speed video camera recorded the spray characteristics of different volatile fuels in a constant-volume combustion bomb. The effects of different rail pressures and ambient back pressures on the spray characteristics were investigated. Engine test: The combustion and emission characteristics of different volatile diesel fuels under different load conditions (25%, 50%, 75%) were investigated in a four-stroke direct-injection diesel engine with the engine speed fixed at 2000 rpm. The test results show that as the rail pressure increases and the ambient pressure decreases, the spray characteristics of the fuels tend to increase; for the more volatile fuels, although reducing the spray tip penetration, the spray projected area and spray cone angle increase, which is conducive to improving the homogeneity of the fuel and air mixing in the cylinder. The improvement of fuel volatility can form more and better-quality mixtures within the ignition delay time (ID), resulting in a 1–2% increase in peak cylinder pressure and a 2–4% increase in peak heat release. For different loads, pre-injection heat release is generated to redefine the ID and combustion duration (CD). Improved fuel volatility effectively reduces carbon monoxide (CO) emissions by about 8–10% and hydrocarbon (HC) emissions by about 13–16%, but it increases nitrogen oxide (NOx) emissions by about 8–11%. Analyzing from the perspective of particulate matter (PM), combined with the aromatic content of volatile fuels, it is recommended to use fuels with moderate volatility and aromatic content under low load conditions, and at medium to large loads, the volatility of the fuel has less weight on particulates and more weight on aromatics, so it is desirable to use the fuel with the lowest volatility and lowest aromatic content of the fuel selected.

Numerical investigation and optimization of the ammonia/diesel dual fuel engine combustion under high ammonia substitution ratio

This study investigated the effects of initial temperature, equivalence ratio, and diesel injection timing on engine combustion and emission characteristics at high ammonia substitution ratios. Increased compression temperature and pressure significantly reduce ignition delay, enhance combustion speed and efficiency, and decrease N2O and unburned NH3 emissions. A strong correlation exists between the amount of N2O produced and the mass of unburned NH3 when ammonia combustion efficiency is high. The N2O distribution is concentrated near the cylinder walls and the bottom surface of the piston platform, in areas with high concentrations of unburned NH3. As the equivalence ratio increases from 0.6 to 0.75, flame propagation speed and indicated thermal efficiency (ITE) increase, while NOx, N2O, and unburned NH3 emissions decrease. The combustion performance and emissions were optimized by advancing the diesel injection timing and increasing the equivalence ratio to accelerate the combustion speed. This adjustment increases ITE to 47.6% at an 80% ammonia energy ratio. Post-optimization results show a reduction in unburned NH3 emissions from 51.7 g/kW·h to 5.9 g/kW·h and a decrease in N2O emissions from 0.930 g/kW·h to 0.370 g/kW·h, culminating in a 60.4% reduction in greenhouse gas (GHG) emissions.

Study of the Combustion Characteristics of a Compression Ignition Engine Fueled with a Biogas–Hydrogen Mixture and Biodiesel

Increasing the use of renewable energy sources is essential to reduce the use of fossil fuels in internal combustion engines and to reduce greenhouse gas emissions. An experimental and numerical simulation study of the combustion process of a compression ignition engine was carried out by replacing fossil diesel with a dual fuel produced from renewable energy sources. In conventional dual-fuel applications, fossil diesel is used to initiate the combustion of natural gas or petroleum gas. In the present study, fossil diesel was replaced with advanced biodiesel – hydrotreated vegetable oil, and natural gas was replaced with biogas. In the experimental study, a gas mixture of 60% natural gas (by volume) and 40% carbon dioxide (by volume) was used to replicate the biogas while maintaining a 40%, 60%, and 80% gas energy share in the fuel. It was observed that using fossil diesel and biogas in the dual-fuel engine significantly slowed down the combustion process, which normally resulted in poorer energy performance. One way to compensate for the lack of energy (due to the presence of carbon dioxide) in the cylinder is to use a gas such as hydrogen, which has a high energy content. To analyze the effect of hydrogen on the dual-fuel combustion process, hydrogen gas was added to the replicated biogas at 10%, 20%, and 30% of the natural gas volume, maintaining the biogas at a (natural gas + hydrogen)-to-carbon dioxide volume ratio of 60%/40% and the expected gas energy share. The combustion process analysis, which was conducted using the AVL BOOST software (Austria), determined the heat release rate, temperature, and cylinder pressure rise in the dual-fuel operation with different renewable fuels and compared the results with those of fossil diesel. It was found that when the engine was operated at medium load and with the flammability of the biogas approaching the limit, the addition of hydrogen significantly improved the combustion characteristics of the dual-fuel engine.

Numerical Investigation of Combustion and Emission Characteristics of the Single-Cylinder Diesel Engine Fueled with Diesel-Ammonia Mixture

This study proposes a dual-fuel approach combining diesel and ammonia in a single-cylinder compression ignition engine to reduce harmful emissions from internal combustion. Diesel is directly injected into the combustion chamber, while ammonia is introduced through the intake manifold with intake air. In this study, injection timing and the percentage of ammonia energy fraction was varied. A computational fluid dynamics (CFD) model simulates the combustion and emission processes to assess the impact of varying diesel injection timings and ammonia energy contributions. Findings indicate that as ammonia content increases, the engine experiences reductions in peak in-cylinder pressure, temperature, heat release rate, as well as overall efficiency and power output. Emission results suggest that greater ammonia usage leads to a reduction in soot, carbon monoxide, carbon dioxide, and unburned hydrocarbons, though a slight increase in nitrogen oxides emissions is observed. This analysis supports ammonia’s potential as a low-emission alternative fuel in future compression ignition engines.

Experimental Investigation on Combustion Characteristics of LHR and Conventional Engines Using Tobacco and Cotton Seed Methyl Ester Blend

This study presents an experimental investigation into the combustion characteristics of Tobacco Seed Oil Methyl Ester (TSOME), Cotton Seed Oil Methyl Ester (CSOME) and its blend (TCOME) as alternatives fuel in both conventional and Low Heat Rejection (LHR) engines. The LHR engine, integrating thermal barrier Ni90 insert is inserted on piston crown to enhance combustion efficiency by reducing heat loss. The work focuses on comparing key combustion parameters such as in-cylinder pressure and heat release rate (HRR) for TSOME, CSOME and its blend in both engines across varying load conditions. The experimental results indicate that both biodiesel fuels and its blend demonstrate good combustion characteristics near to conventional diesel. The LHR engine with blend outperformed compare to the conventional engine of higher peak pressures and heat releasing rate compared to CSOME and TSOME. Peak inside cylinder pressure and heat releasing rate occurred for both engines at 80% of load, for LHR engine peak pressure is 10% high and similarly heat releasing rate is 13% high compare to conventional engine. The present work suggests that the combination of LHR engine with blend of TSOME and CSOME offer a viable solution for improving engine combustion efficiency while reducing consumption of conventional fuels.

Exploring Hydrogen–Diesel Dual Fuel Combustion in a Light-Duty Engine: A Numerical Investigation

Dual fuel combustion has gained attention as a cost-effective solution for reducing the pollutant emissions of internal combustion engines. The typical approach is combining a conventional high-reactivity fossil fuel (diesel fuel) with a sustainable low-reactivity fuel, such as bio-methane, ethanol, or green hydrogen. The last one is particularly interesting, as in theory it produces only water and NOx when it burns. However, integrating hydrogen into stock diesel engines is far from trivial due to a number of theoretical and practical challenges, mainly related to the control of combustion at different loads and speeds. The use of 3D-CFD simulation, supported by experimental data, appears to be the most effective way to address these issues. This study investigates the hydrogen-diesel dual fuel concept implemented with minimum modifications in a light-duty diesel engine (2.8 L, 4-cylinder, direct injection with common rail), considering two operating points representing typical partial and full load conditions for a light commercial vehicle or an industrial engine. The numerical analysis explores the effects of progressively replacing diesel fuel with hydrogen, up to 80% of the total energy input. The goal is to assess how this substitution affects engine performance and combustion characteristics. The results show that a moderate hydrogen substitution improves brake thermal efficiency, while higher substitution rates present quite a severe challenge. To address these issues, the diesel fuel injection strategy is optimized under dual fuel operation. The research findings are promising, but they also indicate that further investigations are needed at high hydrogen substitution rates in order to exploit the potential of the concept.

Impact of nano cerium oxide addition with pyrolysis waste plastic oil on combustion, performance and emission characteristics of CRDI diesel engine

Abstract This investigation examined the effect of incorporating cerium oxide (CeO2) nanoparticle into diesel and waste plastic oil (WPO) blends on the combustion, performance and emission characteristics of the diesel engine. The WPO was extracted from low density polyethylene using plastic pyrolysis. The blending of diesel and WPO with combination of D70:WPO30 and D50:WPO50 was prepared to evaluate the engine operation. Additionally, the spherical sized CeO2 with 50 mg/L and 100 mg/L was added with this blend. The various blends named as Diesel, D-WPO30, D-WPO30+Ce50, D-WPO30+Ce100, D-WPO50, D-WPO50+Ce50 and D-WPO50+Ce100 were used in this investigation to operate the engine under various load conditions. The experiment was performed using water cooled common rail direct injection (CRDI) diesel engine with prepared D-WPO blend. Different characteristics such as In-cylinder pressure (CP), heat release rate (HRR), ignition delay time (IDT), brake thermal efficiency (BTE), brake specific fuel consumption (BSFC) and exhaust gas temperature (EGT), carbon monoxide (CO), hydrocarbon (HC), nitrogen oxide (NOx) and smoke opacity emission are studied with respect to the effect of different blends and applied load used. It was observed that increasing of CeO2 nanoparticles in blend improved the overall performance and emission of the engine. Form the results, D-WPO30+Ce100 blend showed enhanced brake thermal efficiency (BTE), brake specific fuel consumption (BSFC) and exhaust has temperature (EGT) are 28.2%, 3% and 465oC respectively. Similarly, reduced emission of CO, NOx, HC and smoke opacity was observed in the CeO2 added blends particularly at 100 mg/L. It was concluded that among all blends prepared, the D70:WPO30 with 100 mg/L of CeO2 showed improved combustion, performance and emission characteristics in proposed diesel engine.

Experimental Study on the Effect of Ammonia on Combustion and Emission Characteristics of a Spark Ignition Engine Fueled with Hydrogen.

Using hydrogen and its compounds as fuel is one of the key ways to achieve zero carbon emissions in internal combustion engines. Due to the difference in fuel properties of hydrogen and ammonia, mixing the two can make up for each other's shortcomings in combustion performance. Therefore, this paper studies the effects of ammonia addition on the combustion and emission characteristics of a SI commercial hydrogen engine, and studies the differences in these effects under different excess air ratios. The results indicate that increasing the ammonia mass ratio lengthens both flame development and combustion duration, causing a delay in the combustion center. Under stoichiometric conditions, combustion instability increases, peak cylinder pressure and heat release rate decrease significantly, and exhaust temperatures rise. With a higher ammonia mass ratio, brake-specific fuel consumption first decreases and then increases, reaching a minimum at a 0.4-0.6 ammonia mass ratio. Unburned ammonia and N2O emissions gradually increase, while NO X emissions initially rise and then fall, peaking at a low ammonia mass ratio. From the perspective of balancing emissions and fuel economy, for hydrogen-ammonia mixed combustion engines, a 0.6 ammonia mass ratio is recommended under stoichiometric conditions, while lean burn conditions allow for a higher ammonia mass ratio.

Investigations of diesel and natural gas injection interaction on combustion characteristics of a high-pressure direct-injection dual-fuel engine based on large eddy simulation

HPDI (high-pressure direct-injection) with pilot ignition is modern technology developed for heavy-duty natural gas engines. The dynamics of coherent flow structures due to diesel and natural gas jet play a significant role on ignition characteristics. In this study, a large eddy simulation (LES) framework coupled with chemistry solver is conducted for three-dimensional modelling of the thermal process of a HPDI engine. By integrating the Dynamic Mode Decomposition (DMD) algorithm, the break-up and attenuation process of unstable flow structures accompanied by different scale vortex formation and dissipation is able to be effectively demonstrated from fuel jet. The prime in-cylinder flow field structures from natural gas injection to its ignition is characterized by the vortex entrainment phenomenon resulting from the impingement between the natural gas jet and active products from diesel combustion. This phenomenon leads to enhanced heat transfer and exchange of active radicals by which the ignition of the natural gas is therefore facilitated, especially when angle β (the intersection angle between diesel and nature gas jet) is decreased. Moreover, the present study extends the ability of reaction-rate based global pathway analysis to evaluate the reactivity of OH additions to CH4/air mixture. In summary, the interactive dual fuel turbulent combustion process of the HPDI engine is theoretically elucidated, wherein the synergetic kinetics of vortex entrainment-mixing and chemical reaction facilitate the ignition of low reactivity natural gas.

Effects of isopropanol-butanol-ethanol on the performance, combustion and emission characteristics of a diesel-methanol dual-fuel engine

Both diesel-methanol dual-fuel (DMDF) combustion and the addition of isopropanol-butanol-methanol (IBE) into diesel are capable of reducing the fossil fuel usage and soot emissions of diesel engines, but few of studies focused on combining the advantages of these two methods. Thereby, diesel containing 10 %, 20 % and 30 % of IBE by volume were utilized as pilot fuel in this study to investigate how the addition of IBE into diesel affects the performance, combustion and emissions of the DMDF engine. Experiments were performed at the engine load of 20 %, 40 % and 60 % with the engine speed fixed at 1400r/min. The results show that at most test conditions, the brake thermal efficiency of the DMDF engine only suffers a slightly drop while the soot emissions greatly reduce when IBE is blended into the pilot fuel diesel. Moreover, the deterioration of CO, HC and NOx emissions of DMDF engine can be significantly improved by blending no more than 20 % vol. IBE into the pilot fuel diesel. Additionally, with the volume ratio of IBE into the pilot fuel diesel increases to 30 %, the soot emissions of the DMDF engine can be further reduced at the costs of engine performance deteriorates and CO, HC, NOx emissions increase. Although the deterioration of the engine performance caused by the addition of IBE into the pilot fuel diesel can be mitigated by increasing the methanol flow rate, NOx emissions increase significantly.

Production of oxy-hydrogen with an alkaline electrolyzer, and its impacts on engine behaviors fuelled with diesel/waste fish biodiesel mixtures supported by graphene-added nanofuels

Because of the high viscosity, low calorific value, atomization, and vaporization problems of biodiesel, addition of nano additives with oxyhydrogen is encouraged to improve engine combustion and emissions. Waste fish methyl ester was blended with diesel oil in 20%, and then nano graphene was added to diesel-biodiesel mixtures at doses of 25, 50, and 100 mg/L. An alkaline electrolyzer was employed to generate oxyhydrogen gas at a rate of 0.5 liters per minute through water electrolysis. At 3000 rpm rated speed and engine load range from 25 to 100% with the interval of 25% were investigated. Mixtures of graphene in methyl ester combinations have increased the thermal efficiency of biodiesel blend by 11%, 13%, and 15%, respectively, when supplemented with HHO. The addition of 25, 50, and 100 ppm of graphene to the methyl ester was mixed along with oxyhydrogen, resulting in notable reductions of CO emissions by 18%, 22%, and 25% for WF20. Significant decreases in HC emissions by 29%, 32%, and 38%, accompanied by noticeable declines in smoke concentrations of 25%, 28%, and 33% for WF20G25 + HHO, WF20G50 + HHO, and WF20G100 + HHO were shown. Moreover, NOx emissions experienced reductions of 20%, 24%, and 29% when HHO was added to methyl ester blends containing 25, 50%, and 100 ppm of graphene, respectively. Incorporating biodiesel from waste fish oil, enriched with 100 ppm graphene with HHO shows potential for lowering exhaust emissions, and enhancing engine performance and combustion characteristics, particularly for the commonly used biodiesel with poor fuel properties.

Enhancing Combustion Efficiency: Utilizing Graphene Oxide Nanofluids as Fuel Additives with Tomato Oil Methyl Ester in CI Engines

The research aims to conduct a thorough examination of the combustion, injection, performance, and emission characteristics of a diesel engine below different engine loads, as well as the synthesis of graphene oxide (GO) nano fuels and their utilization in combination with Tomato Oil methyl ester (TOME) and diesel fuel blend. The graphene oxide, plays a vital role in the pre-mixed combustion phase of diesel engines. Addition of graphene oxide nano fuels enhances the high-pressure combustion stage, resulting in increased maximum pressure and heat release rate. TOME (B20GO75) and TOME (B20GO100) exhibit comparable heat release rate to diesel due to improved fuel characteristics and quicker ignition delay duration. While TOME (B20) shows a slight decrease in (BTE) compared to diesel, the addition of graphene oxide improves BTE, with TOME (B20GO50) displaying the highest BTE at full load, indicating enhanced combustion efficiency. Moreover, graphene oxide addition leads to a reduction in carbon monoxide (CO) and hydrocarbon (HC) emissions, with emissions decreasing as the concentration of graphene oxide increases. However, NoX emissions initially decrease with TOME (B20) compared to diesel but increase with higher graphene oxide concentration. Smoke emissions increase with TOME (B20) but decrease with higher graphene oxide dosages. Overall, the incorporation of graphene oxide nano fuels into Tomato Oil methyl ester blends demonstrates potential for improving engine performance and reducing emissions.

Impact on Green Synthesised Al2O3 Nanoparticles on Performance and Emission Properties as Biodiesel operated diesel engine

<p style="text-align:justify;"><span style="font-family:"Times New Roman","serif";font-size:12pt;line-height:150%;">Global warming and pollution are two of the numerous causes of environmental issues due to industrial wastes and greenhouse gases. As a result, efforts are being made to limit emissions in order to mitigate these issues and reduce pollution. Given that fuel supplies are running low, biodiesel is one of the best alternatives to diesel fuel. One of the main obstacles to biodiesel's commercialization is its higher cost than diesel. One of the more superior substitute fuels for diesel is biodiesel, which is a fuel with great potential. When combined with 20% commercial diesel (B20), the resulting biodiesel is known as Pongamia. Improving engine performance and combustion characteristics while decreasing atmospheric NOX, CO, and HC exhaust emissions are the primary goals of this research. In comparison to neat diesel, BSFC and BTE were found to have increased by 12.27% and 15.34% respectively, while NOx, CO, and HC concentrations were decreased by 15.46%, 54%, 7.30%, and 25.67% respectively. Biodiesel mixed with Al<sub>2</sub>O<sub>3</sub> nano additive significantly improves the performance and combustion characteristics of diesel engines.</span></p>

Effect of pre-chamber volume and nozzle number on turbulent jet combustion characteristics of GDI engines

There are few studies on the effect of turbulent jets on the combustion characteristics of passive pre-chamber (PC) gasoline engines, and their mechanism needs to be elucidated. Therefore, a 3-D simulation was performed using CONVERGE software. The results reveal that a modest expansion in the PC volume contributes to combustion due to the increased jet energy, but when it is too large, the above effect is weakened. In this study, at a smaller 0.8 ml volume, the combustion is still similar to traditional spark plug ignition. At middle 1.6 ml volume, the mixture concentration in the PC increases and the uniformity is better, resulting in the highest jet velocity and shortest jet duration, thus achieving the fastest flame propagation and the highest heat release rate (HRR). However, at a larger 1.8–2.0 ml volume, the mixture concentration near the spark-plug is sharply reduced, thus the reduced combustion rate in the PC leads to insufficient jet energy in the subsequent jets and resulting deterioration in combustion. An appropriate increase in nozzle number also improves combustion by introducing more ignition sources. But more nozzles not always improving the combustion. In the eight-nozzle case, three nozzles are close to the exhaust valve so that the intake is inhibited, resulting in a worsening of the ignition. The combustion under six-nozzle shows the highest HRR and shortest combustion duration. However, the combustion deteriorates at eight-nozzle, since the increase in the ignition point is not enough to compensate for the negative impact of the reduced jet intensity on combustion.

Experimental multiple parameters optimization of the injection strategies for a turbocharged direct injection hydrogen engine to achieve highly efficient and clean performance

Improving the brake thermal efficiency (BTE) and reducing NOx emissions are two main goals for hydrogen-powered internal combustion engines to achieve efficient and clean performance. This paper focuses on the multiple parameters optimization of injection and ignition both experimentally and numerically based on a 2.0L turbocharged direct injection hydrogen engine. Firstly, the effects of single and split injection on engine performance, in-cylinder mixing and combustion characteristics are investigated. Secondly, the single-factor effect of split injection parameters and spark timing on engine performance are obtained with different engine speeds. Significant interaction effects are detected between these factors. Thus, a multi-parameter optimization is conducted based on the response surface methodology method to analyze the co-relationship of factors (split injection control parameters and ignition) on responses (BTE, NOx emissions, and knock intensity) at high-load. Finally, a maximum BTE of 43.03 % and a reduction in NOx emissions by 71.19 % are achieved with the help of model prediction at 2500 rpm and a load of 1.40 MPa. Further optimization of other engine speeds is conducted, and the boundary of high-efficiency region (BTE>40 %) covers over 50 % of the load map after optimization. These results can provide valuable support for the performance improvement of efficiency and clean hydrogen engines.

Combustion characteristics of methanol engine applying TJI-HPDI with optimized pre-chamber nozzle structure under different injection and spark strategy

Methanol fuel faces challenges in achieving mixing controlled combustion (MCC) due to its low cetane number. This study proposes utilizing turbulent jet ignition to facilitate methanol MCC under high-pressure direct injection mode, namely TJI-HPDI. Three coordination schemes were developed numerically based on the projection angles between hot jets and main methanol spray plumes axis: opposing (Base design), opposing staggered (Design 1), and circumferential staggered interference (Design 2). Varied orifice diameters was employed to regulate jet energy and velocity. The results indicated that Design 2-BSB (Big-Small-Big orifice) scheme exhibited superior combustion and emission performance. Furthermore, the impact of start of main injection timing (SOI) on ignition and combustion characteristics was investigated under this scheme. An SOI of −12 °CA after top dead center (TDC), creating a 7 °CA interval between spark and SOI timing, achieved optimal ITE by minimizing the duration of CA10-CA50 and optimization methanol mixture distribution around hot jets. Additionally, pre-chamber (PC) spark ignition timing (ST) effects were also explored, with the optimal timing at −8 °CA ATDC. ST has minimal impact on heat release rate (HRR), because high-energy jets could ensure rapid and stable combustion. Moreover, the combustion stability of TJI-HPDI was demonstrated, underscoring the importance in understanding and optimizing TJI-HPDI ignition processes.

Effect of ammonia reforming on combustion and emission characteristics of a 4-valve engine with an active pre-chamber

Ammonia (NH3), as a hydrogen carrier and carbon-free fuel, offers an attractive opportunity for engines to achieve carbon neutrality. Turbulent jet ignition (TJI) combined with ammonia reforming shows the great capacity in ammonia-fueled engines. In this study, the effects of reforming strategy in an ammonia-fueled TJI are numerically studied, addressing the reforming ratio and reforming region. The results show that when only using reformate in the pre-chamber, the promoting effect of jet flame is more effective on the initial combustion phase. There are still very high NH3 emissions due to the low reactivity in the main chamber. Further using reformate both in the pre-chamber and the main chamber, all the combustion stages (ST-CA10, CA10-50, CA50-90) can be shortened almost linearly with the increase of reforming ratio. Besides, the unburned NH3 can be reduced to an acceptable level when the reforming ratio reaches 200 ‰ (hydrogen energy ratio of 18.50 %). The main reason is that the jet-induced strong flow field is coincident with the whole combustion stage. Further increasing the reforming ratio (pure hydrogen) in the pre-chamber, a high combustion efficiency and acceptable NH3 emission can be achieved at a low hydrogen energy ratio (7.08 %). However, knocking combustion will happen at high reforming ratio with a low knock intensity. The results can provide some guidance for making the best-promoting benefit of the limited hydrogen in ammonia TJI engines with different reforming strategies.

Investigating the Effect of Ammonia Addition on the Performance of a Heavy-Duty Natural Gas Spark Ignition Engine Operated at Stoichiometric Conditions

Abstract Due to the pressing issue of global warming, there has been a significant focus on zero- and low-carbon fuels globally. Among hydrocarbon fuels, methane is widely used in spark ignition engines due to its abundance and relatively low carbon footprint. However, to further reduce carbon emissions, interest is growing in the use of ammonia, a zero-carbon fuel, as a partial replacement for methane. Consequently, it is crucial to investigate the impact of ammonia addition on the performance of natural gas spark ignition engines. A key challenge in studying ammonia-methane engines is that the introduction of ammonia alters the formation mechanisms of nitrogen-based pollutants, resulting in the coupling of fuel-borne and air-borne nitrogen pollutants. As a result, research on the nitrogen-based emissions of ammonia-methane engines has been limited. This study addresses this issue by differentiating between atmospheric nitrogen and fuel nitrogen elements, effectively decoupling fuel-borne and air-borne nitrogen pollutants. This approach provides valuable insights into the effects of ammonia addition on the nitrogen-based pollutant characteristics of natural gas engines. The results indicate that ammonia addition introduces N2O, a species absent in pure methane engines. The N2O primarily originates from cold wall regions and the partial oxidation of ammonia released from engine crevices during the late oxidation process. Although NO remains the dominant nitrogen-based pollutant and the amount of N2O is small, the significant greenhouse gas potential of N2O warrants further attention. Furthermore, while ammonia addition increases the NO concentration in the burning zone, it slightly reduces the NO concentration at chemical equilibrium under stoichiometric conditions. As a result, engines operating with an ammonia energy substitution ratio of 0.4 exhibit lower NOx emissions compared to those fueled solely by methane. These findings underscore the need for further research into the combustion and emission characteristics of ammonia-methane spark ignition engines.

Effects of different gas energy shares on combustion and emission characteristics of compression ignition engine fueled with dual-fossil fuel and dual-biofuel

This study systematically investigates the energetic and environmental performance of a four-cylinder compression ignition (CI) engine fueled by gaseous and liquid dual-fuel (D-F), utilising various combinations of fossil fuels and biofuels. Fossil diesel or pure hydrotreated vegetable oil (HVO) – new generation biodiesel was used as the pilot fuel to initiate ignition of the gaseous fuel. The gaseous fuels used were natural gas (NG) and simulated biogas (BG) composed of 60 % NG and 40 % CO2 by volume, injected into the intake manifold at varying gas energy shares (GES) of 40 %, 60 %, and 80 %. Reference values were provided from conventional combustion of diesel fuel and HVO. This study used numerical simulations to examine indicators of combustion, such as ignition delay, premixed combustion phase, diffusion combustion phase, and subsequent combustion phases, across diverse fuel combinations. Within lean dual-fuel mixtures, when the gaseous fuel remained below the flammability threshold, the peak pressure was diminished, the rate of pressure rise was lowered, and the combustion process decelerated, facilitating a faster transition to the diffusion phase. As the engine load and GES increased, the excess air ratio decreased, bringing the air-fuel mixture closer to the flammability limit, which in turn altered the combustion characteristics and engine performance trends. Combustion with increasing BG content showed partial similarities to that of NG, though the high CO2 content in biogas was found to suppress combustion, functioning similarly to an exhaust gas recirculation. The study also compared brake thermal efficiency (BTE), as well as specific emissions of CO, HC, NOX, CO2, and smoke for the D-F engine operation against pure diesel and HVO at different loads and GES levels. Additionally, an overlimit function was used to assess the emission levels of D-F engines with reference to emission limits.

Synergy effect of nozzle structure and pre-chamber reactivity on the combustion characteristics of ammonia engines

Ammonia (NH3) offers an attractive opportunity for internal combustion engines (ICE) to be carbon–neutral. An active pre-chamber fueled with hydrogen might be suitable to overcome the poor combustion characteristics of ammonia engines. The primary goal of this work is to numerically study the combustion characteristics of ammonia engines with a hydrogen-fueled pre-chamber, and the synergy effect of nozzle structure and pre-chamber reactivity (hydrogen quantity) are also considered. The results show that the hydrogen fraction is reduced to a low degree in the pre-chamber because of the scavenging process. Thus, it is better to inject hydrogen into the pre-chamber during the compression stroke. Although high pre-chamber reactivity is effective in improving the main chamber combustion, a multi-hole pre-chamber is needed to get the maximum promoting effect of the high reactivity when compared to the single-nozzle pre-chamber. For multi-hole pre-chamber, 2 mm is the recommended nozzle diameter when considering the promoting effect, and the recommended area-volume ratio (nozzle number) is increased with the pre-chamber reactivity. For nitrogen-based emissions, the distribution strongly depends on the flame characteristics. High pre-chamber reactivity can significantly reduce the NH3 emissions, while NO emissions will increase with the pre-chamber reactivity. The current study can give some insights and be a preface for the development of ammonia engines.