A computational study to analyze the effect of equivalence ratio and hydrogen volume fraction on the ultra-lean burning of the syngas-fueled HCCI engine

This computational study investigates the equivalence ratio and hydrogen volume fraction effect on the ultra-lean burning of the syngas-fueled homogeneous charge compression ignition (HCCI) engine. In this research, low calorific syngas, composed of different compositions of H2, CO, and CO2, is used as a fuel in the HCCI engine that is operated under an overly lean air-fuel mixture. ANSYS Forte CFD package with Gri-Mech 3.0 chemical kinetics was used to analyze the in-cylinder combustion phenomena, and the simulation results were validated with experimental tests in the form of in-cylinder pressure and heat release rate at different equivalence ratios.The results indicate that changing the equivalence ratio produces a negligible change in combustion phasing, while it positively impacts the combustion and thermal efficiency of this syngas-fueled HCCI engine under lean conditions due to the high burning rate in the squish region. Moreover, an increased equivalence ratio increases MPRR due to the rich mixture combustion. The results also represent that the high-volume fraction of H2 in syngas fuel causes an advanced burning phase, improves the combustion performance of the HCCI engine at all equivalence ratio conditions, and causes slightly high NOx emissions.     

Effect of syngas composition on combustion and exhaust emission characteristics in a pilot-ignited dual-fuel engine operated in PREMIER combustion mode

The objective of this study was to investigate the performance and emissions of a pilot-ignited, supercharged, dual-fuel engine powered by different types of syngas at various equivalence ratios. It was found that if certain operating conditions were maintained, conventional engine combustion could be transformed into combustion with two-stage heat release. This mode of combustion has been investigated in previous studies with natural gas, and has been given the name PREmixed Mixture Ignition in the End-gas Region (PREMIER) combustion. PREMIER combustion begins as premixed flame propagation, and then, because of mixture autoignition in the end-gas region, ahead of the propagating flame front, a transition occurs, with a rapid increase in the heat release rate. It was determined that the mass of fuel burned during the second stage affected the rate of maximum pressure rise. As the fuel mass fraction burned during the second stage increased, the rate of maximum pressure rise also increased, with a gradual decrease in the delay between the first increase in the heat release rate following pilot fuel injection and the point when the transition to the second stage occurred. The H₂ and CO₂ content of syngas affected the engine performance and emissions. Increased H₂ content led to higher combustion temperatures and efficiency, lower CO and HC emissions, but higher NOx emissions. Increased CO₂ content influenced performance and emissions only when it reached a certain level. In the most recent studies, the mean combustion temperature, indicated thermal efficiency, and NOx emissions decreased only when the CO₂ content of the syngas increased to 34%. PREMIER combustion did not have a major effect on engine cycle-to-cycle variation. The coefficient of variation of the indicated mean effective pressure (COV_IMEP) was less than 4% for all types of fuel at various equivalence ratios, indicating that the combustion was within the stability range for engine operation.     

Modelling of hydrogen-blended dual-fuel combustion using flamelet-generated manifold and preferential diffusion effects

In the present study, Reynolds-Averaged Navier-Stokes simulations together with a novel flamelet generated manifold (FGM) hybrid combustion model incorporating preferential diffusion effects is utilised for the investigation of a hydrogen-blended diesel-hydrogen dual-fuel engine combustion process with high hydrogen energy share. The FGM hybrid combustion model was developed by coupling laminar flamelet databases obtained from diffusion flamelets and premixed flamelets. The model employed three control variables, namely, mixture fraction, reaction progress variable and enthalpy. The preferential diffusion effects were included in the laminar flamelet calculations and in the diffusion terms in the transport equations of the control variables. The resulting model is then validated against an experimental diesel-hydrogen dual-fuel combustion engine. The results show that the FGM hybrid combustion model incorporating preferential diffusion effects in the flame chemistry and transport equations yields better predictions with good accuracy for the in-cylinder characteristics. The inclusion of preferential diffusion effects in the flame chemistry and transport equations was found to predict well several characteristics of the diesel-hydrogen dual-fuel combustion process: 1) ignition delay, 2) start and end of combustion, 3) faster flame propagation and quicker burning rate of hydrogen, 4) high temperature combustion due to highly reactive nature of hydrogen radicals, 5) peak values of the heat release rate due to high temperature combustion of the partially premixed pilot fuel spray with entrained hydrogen/air and then background hydrogen-air premixed mixture. The comparison between diesel-hydrogen dual-fuel combustion and diesel only combustion shows early start of combustion, longer ignition delay time, higher flame temperature and NOx emissions for dual-fuel combustion compared to diesel only combustion.     

6105ZQS双燃料发动机的开发及试验研究

针对6105ZQ增压中冷发动机开发出了610SZQS柴油-天然气双燃料发动机。为了进一步对6105ZQ双燃料发动机进行性能研究，针对燃烧室结构参数、供油提前角、天然气替代率等对双燃料发动机性能有重要影响的因素进行了试验，研究其对发动机性能、缸内压力升高率、放热率以及缸内温度的影响，为今后开发天然气电控喷射式双燃料发动机及提高其性能提供依据。     

Performance and emissions of a supercharged dual-fuel engine fueled by hydrogen-rich coke oven gas

This study investigated the engine performance and emissions of a supercharged dual-fuel engine fueled by hydrogen-rich coke oven gas and ignited by a pilot amount of diesel fuel. The engine was tested for use as a cogeneration engine, so power output while maintaining a reasonable thermal efficiency was important. Experiments were carried out at a constant pilot injection pressure and pilot quantity for different fuel-air equivalence ratios and at various injection timings without and with exhaust gas recirculation (EGR). The experimental strategy was to optimize the injection timing to maximize engine power at different fuel-air equivalence ratios without knocking and within the limit of the maximum cylinder pressure. The engine was tested first without EGR condition up to the maximum possible fuel-air equivalence ratio of 0.65. A maximum indicated mean effective pressure (IMEP) of 1425 kPa and a thermal efficiency of 39% were obtained. However, the nitrogen oxides (NOx) emissions were high. A simulated EGR up to 50% was then performed to obtain lower NOx emissions. The maximum reduction of NOx was 60% or more maintaining the similar levels of IMEP and thermal efficiency. Two-stage combustion was obtained; this is an indicator of maximum power output conditions and a precursor of knocking combustion.     

Performance and emission comparison of a supercharged dual-fuel engine fueled by producer gases with varying hydrogen content

This study investigated the effect of hydrogen content in producer gas on the performance and exhaust emissions of a supercharged producer gas–diesel dual-fuel engine. Two types of producer gases were used in this study, one with low hydrogen content (H₂ = 13.7%) and the other with high hydrogen content (H₂ = 20%). The engine was tested for use as a co-generation engine, so power output while maintaining a reasonable thermal efficiency was important. Experiments were carried out at a constant injection pressure and injection quantity for different fuel–air equivalence ratios and at various injection timings. The experimental strategy was to optimize the injection timing to maximize engine power at different fuel–air equivalence ratios without knocking and within the limit of the maximum cylinder pressure. Two-stage combustion was obtained; this is an indicator of maximum power output conditions and a precursor of knocking combustion. Better combustion, engine performance, and exhaust emissions (except NO_x) were obtained with the high H₂-content producer gas than with the low H₂-content producer gas, especially under leaner conditions. Moreover, a broader window of fuel–air equivalence ratio was found with highest thermal efficiencies for the high H₂-content producer gas.     

Modeling study on the production of hydrogen/syngas via partial oxidation using a homogeneous charge compression ignition engine fueled with natural gas

The production of hydrogen and syngas from natural gas using a homogeneous charge compression ignition reforming engine is investigated numerically. The simulation tool used was CHEMKIN 3.7, using the GRI-3 natural gas combustion mechanism. This simulation was conducted on the changes in hydrogen and syngas concentration according to the variations of equivalence ratio, intake temperature, oxygen enrichment, engine speed, initial pressure, and fuel additives with partial oxidation combustion. The simulation results indicate that the hydrogen/syngas yields are strongly dependent on the equivalence ratio with maxima occurring at an optimal equivalence ratio varying with engine speed. The hydrogen/syngas yields increase with increasing intake temperature and oxygen contents in air. The hydrogen/syngas yields also increase with increasing initial pressure, especially at lower temperatures, yet high temperature can suppress the pressure effect. Furthermore, it was found that the hydrogen/syngas yields increase when using fuel additives, especially hydrogen peroxide. Through the parametric screening studies, optimum operating conditions for natural gas partial oxidation reforming are recommended at 3.0 equivalence ratio, 530 K intake temperature, 0.3 oxygen enrichment, 500 rpm engine speed, 1 atm initial pressure, and 7.5% hydrogen peroxide.     

Research on emission characteristics of hydrogen fuel internal combustion engine based on more detailed mechanism

A CFD simulation model with simplified chemical reaction mechanism was built based on CONVERGE software to study the in-cylinder combustion progress and NO generation mechanism of hydrogen fueled internal combustion engine (HICE). Simulation results show that the in-cylinder combustion progress experiences the ellipsoidal flame stable propagation stage and the rapid turbulent combustion stage. At the end of rapid turbulent combustion the OH concentration decreases quickly, the peak temperature and maximum NO mass appear at that time, and then the in-cylinder temperature and NO mass decrease step by step. The final emission depends on the peak temperature and NO decomposition time of high-temperature regions. The higher the maximum temperature, the greater the NO peak mass; and the faster the temperature drop, the less the NO decomposes. Adoption of EGR can reduce the in-cylinder maximum temperature, and NO decomposes sufficiently at low speed, which in turn leads to lower NO emission of HICE.     

Heat Transfer in Diesel and Partially Premixed Combustion Engines; A Computational Fluid Dynamics Study

This article presents findings from a Computational Fluid Dynamics (CFD) study performed on the heat transfer characteristics of diesel and partially-premixed combustion (PPC) engines. The study is confined to the combustion bowl, where numerical simulations have been performed on a part of the engine cycle, namely the compression, combustion, and expansion phases. Three engine geometries were simulated and after validating the results with experimental data, parameter variations were carried out, in order to estimate their effects on the heat transfer, engine performance, and emission levels. The work was performed using a commercial CFD tool, with which only a part of the engine cylinder was modeled, the enclosure of one spray. The results highlight some important characteristic differences between the conventional diesel combustion and the low-temperature combustion scheme PPC. The reduced in-cylinder temperatures for the PPC case lead to a reduced production of NO_x and soot emissions, without compromising the engine performance, only a small penalty in the increased intake air pressure is found. The importance of an appropriate injection strategy was also highlighted, as the presence of a pilot injection during the compression stroke enhanced the temperature stratification in a PPC engine. This leads to reduced heat losses and improved engine efficiency. Finally, the shape of the combustion bowl was shown to have significant effects on both heat losses as well as emission levels.     

Assessment of combustion and exhaust emissions in a common-rail diesel engine fueled with methane and hydrogen/methane mixtures under different compression ratio

This study investigates the potential usage of the methane and hydrogen enriched methane in a turbocharged common-rail direct injection diesel engine. Methane and hydrogen/methane mixtures are sent through the air intake manifold of the engine. The engine is operated at four different loads and three different compression ratios. Results are compared amongst single diesel and dual-fuel operations at different compression ratios and load conditions. Compared to diesel, dual-fuel operations mostly generate higher and advanced peak in-cylinder gas pressure, more combustion noise, late pilot injection and start of combustion, advanced combustion center, substantial variations at ignition delay and combustion duration, a significant increase in cyclic variations at low and medium loads, and earlier heat release. Hydrogen enrichment decreases evidently specific fuel consumption. Concerning emissions, compared to diesel operation, dual-fuel operations produce higher total hydrocarbon (THC) and nitrogen oxides (NO_x) but lower carbon dioxide (CO₂). Hydrogen substitutions decrease THC and CO₂ emissions of methane dual-fuel operations approximately between 9-29% and 1–32%, respectively. Smoke emission of dual-fuel operations is less than that of diesel at low and medium loads, whereas it sharply increases at high load. Knocking occurs at high compression ratio and load conditions with dual-fuel operations and dramatically increases with increasing hydrogen ratio. Decreasing the compression ratio notably reduces the combustion noise as well as some emissions, such as NO_x, CO₂ and smoke, for entire load ranges of dual-fuel and diesel operations.     

Comparative study of some experimental methods to characterize the combustion process in a SI engine

Seven common methods based on in-cylinder data, usually applied to determine the combustion parameters (ignition delay and combustion duration), are compared using in-cylinder data provided from a natural gas spark ignition engine operating under lean conditions. The influence of three engine operating parameters: spark advance, throttle opening and fuel/air equivalence ratio, on combustion parameters are tested using every method and the results are compared. The application of these methods on average and individual cycles is also performed. The advantages and disadvantages of these methods are presented and discussed. Some methods can be used only for the ignition delay determination. A comparison with a motor-cycle, so a specific experimental device, is necessary for three methods. Others are very sensitive to noise, or can be used only in some restricted area of engine operating conditions. One method needs calculations based on several experimental assumptions.     

Experimental and computational study on the enhancement of engine characteristics by hydrogen enrichment in a biogas fuelled spark ignition engine

Limitations on the upgradation of biogas to biomethane in terms of cost effectiveness and technology maturity levels for stationary power generation purpose in rural applications have redirected the research focus towards possibilities for enhancement of biogas fuel quality by blending with superior quality fuels. In this work, the effect of hydrogen enrichment on performance, combustion and emission characteristics of a single-cylinder, four-stroke, water-cooled, biogas fuelled spark-ignition engine operated at the compression ratio of 10:1 and 1500 rpm has been evaluated using experimental and computational (CFD) studies. The percentage share of hydrogen in the inducted biogas fuel mixture was increased from 0 to 30%, and engine characteristics with pure methane fuel was considered as a baseline for comparative analysis. The CFD model is developed in Converge CFD software for a better understanding on combustion phenomenon and is validated with experimental data. In addition, the percentage share of hydrogen enrichment which would serve as a compromise between biogas upgradation cost and engine characteristics is also identified. The results of study indicated an enhancement in combustion characteristics (peak in-cylinder pressure increased; COV_IMEP reduced from 9.87% to 1.66%; flame initiation and combustion durations reduced) and emission characteristics (hydrocarbon emissions reduced, and NOx emissions increased but still lower than pure methane) with increase in hydrogen share from 0 to 30% in biogas fuelled SI engine. Flame propagation speed increased and combustion duration reduced with hydrogen supplementation and the same was evident from the results of the CFD model. Performance of the engine increased with increase in hydrogen share up to 20% and further increment in hydrogen share degraded the performance, owing to heat losses and the enhancement in combustion characteristics were relatively small. Overall, it was found that 20% blending of hydrogen in the inducted biogas fuel mixture will be effective in enhancing the engine characteristics of biogas fuelled engines for stationary power generation applications and it holds a good compromise between biogas upgradation cost and engine performance.     

CA6DL1—30柴油机燃烧室改进的模拟与实验研究

为研究燃烧室形状对柴油机燃烧和排放性能的影响,应用大型通用CFD软件STAR—CD程序对3种不同形状的燃烧室内燃烧过程进行了多维数值模拟计算,研究了不同的燃烧室形状对缸内气流运动以及缸内燃烧温度和排放的影响,并通过实验验证了计算模型的正确性。     

基于AVL-FIRE的汽油机缸内滚流的模拟计算

利用三维流体力学软件AVL-FIRE,对495汽油机在不同初始缸内流场条件下的压缩和燃烧过程进行CFD模拟计算。给出了汽油发动机压缩过程中不同初始滚流比下缸内速度场的变化趋势,分析了初始流场中滚流空间位置变化对湍动能场的影响,以及初始流场滚流比对燃烧的影响。     

Combustion,performance and emission analyses of a CI engine operating with renewable diesel fuels (HVO/FARNESANE) under dual-fuel mode through hydrogen port injection

The use of hydrogen in internal combustion engines is pointed out as an alternative to reduce greenhouse gas emissions. In applications that require high levels of torque and low engine speeds, compression ignition (CI) engines are more appropriate. However, because of the high auto-ignition temperature of hydrogen, its use in these engine types is more suitable when the dual-fuel concept is applied. This study comprehensively investigates, through experimental techniques, the use of hydrogen port-injection in a four-stroke single-cylinder CI engine operating with the renewable diesel-like fuels hydrotreated vegetable oil (HVO) and farnesane, in comparison to fossil diesel dual-fuel operation. In this sense, the present work aims to fill a gap in the literature by performing a novel analysis of dual-fuel operation with hydrogen, considering different substitution fractions, and using groundbreaking biofuels, such as HVO and farnesane. The results showed that in-cylinder pressure and temperature were increased with H₂ enrichment for every pilot fuel, but green diesel fuels presented lower values than those for diesel operation. Furthermore, hydrogen port injection slightly delayed the start of combustion and increased the ignition delay, but a reduction in both premixed and diffusion combustion duration was observed. Reductions in PM, CO, and CO₂ emissions were reported during H₂ addition for every pilot fuel, while increased NO_x was observed. Despite this increase, both HVO and farnesane decreased the emissions of this pollutant in single and dual-fuel operations, compared with fossil diesel. In addition, both renewable diesel fuels presented higher BTE than diesel for every studied H₂ mass flow.     

Application of machine learning and Box-Behnken design in optimizing engine characteristics operated with a dual-fuel mode of algal biodiesel and waste-derived biogas

Waste-derived biogas and third-generation algal biodiesel are attractive alternative fuels to substitute fossil diesel in a diesel engine. However, using biodiesel as a pilot liquid fuel and biogas as the main fuel in a diesel engine is a complicated and highly non-linear process. The current study seeks to predict and optimize the combustion and exhaust emission characteristics of a variable compression dual-fuel combustion engine. Data from experiments were obtained at a variety of engine loads, compression ratios, pilot fuel injection pressures, and timings. A multi-layer perceptron network was employed to develop an Artificial Neural Network (ANN) based prognostic model using the experimental data. The developed prognostic model was used to estimate brake thermal efficiency, biogas flow rates, peak in-cylinder pressure, carbon dioxide, unburned hydrocarbons, oxides of nitrogen, and carbon monoxide. The predictive model's robustness is demonstrated by statistical metrics such as R (0.9723–0.988) and R² (0.9453–0.9761), Nash-Sutcliffe model efficiency (94–97%), and mean absolute percentage error (0.013–0.128%), Kling-Gupta efficiency (0.9548–0.9836), and Theil's U2 model uncertainty (0.162–0.368). To optimize the parameters of dual-fuel combustion, the Multi-Output Response Surface Methodology (RSM) was employed. The trade-off assessment between emission and efficiency using the desirability approach revealed that 84% engine load, 244 bar of fuel injection pressure, 28 °BTDC of injection timing, and 17.5 compression ratio are the best-operating conditions for the test engine. An experimental investigation was used to corroborate the RSM research findings, and errors were less than 9%. It was revealed that ANN-linked RSM is a good hybrid technique for modeling, prediction, and optimization of the performance of a dual-fuel engine.     

Effects of fuel combination and IVO timing on combustion and emissions of a dual-fuel HCCI combustion engine

This paper experimentally and numerically studied the effects of fuel combination and intake valve opening (IVO) timing on combustion and emissions of an n-heptane and gasoline dual-fuel homogeneous charge compression ignition (HCCI) engine. By changing the gasoline fraction (GF) from 0.1 to 0.5 and the IVO timing from –15°CA ATDC to 35°CA ATDC, the in-cylinder pressure traces, heat release behaviors, and HC and CO emissions were investigated. The results showed that both the increased GF and the retarded IVO timing delay the combustion phasing, lengthen the combustion duration, and decrease the peak heat release rate and the maximum average combustion temperature, whereas the IVO timing has a more obvious influence on combustion than GF. HC and CO emissions are decreased with reduced GF, advanced IVO timing and increased operational load.     

On the capabilities and limitations of predictive,multi-zone combustion models for hydrogen-diesel dual fuel operation

Compared with traditional hydrocarbon fuels, hydrogen provides a high-energy content and carbon-free source of energy rendering it an attractive option for internal combustion engines. Co-combusting hydrogen with other fuels offers significant advantages with respect to thermal efficiency and carbon emissions.This study seeks to investigate the potential and limitations of multi-zone combustion models implemented in the GT-Power software package to predict dual fuel operation of a hydrogen-diesel common rail compression ignition engine. Numerical results for in-cylinder pressure and heat release rate were compared with experimental data. A single cylinder dual-fuel model was used with hydrogen being injected upstream of the intake manifold. During the simulations low (20 kW), medium (40 kW) and high (60 kW) load conditions were tested with and without exhaust gas recirculation (EGR) and at a constant engine speed of 1500 rpm. Both single and double diesel injection strategies were examined with hydrogen energy share ratio being varied from 0 to 57% and 0–42 respectively. This corresponds to a range in hydrogen air-equivalence ratios of approximately 0–0.29.The results show that for the single-injection strategy, the model captures in-cylinder pressure and heat release rate with good accuracy across the entire load and hydrogen share ratio range. However, it appears that for high hydrogen content in the charge mixture and equivalence ratios beyond the lean flammability limit, the model struggles to accurately predict hydrogen entrainment leading to underestimated peak cylinder pressures and heat release rates. For double-injection cases the model shows good agreement for hydrogen share ratios up to 26%. However, for higher energy share ratios the issue of erroneous hydrogen entrainment into the spray becomes more accentuated leading to significant under-prediction of heat release rate and in-cylinder pressure.     

A combined experimental and numerical study of thermal processes, performance and nitric oxide emissions in a hydrogen-fueled spark-ignition engine

This work concerns the study of a spark-ignition engine fueled with hydrogen, using both measured and numerical data at various conditions, focusing on the combustion efficiency, the heat transfer phenomena and heat loss to the cylinder walls, the performance, as well as the nitric oxide (NO) emissions formed, when the fuel/air and compression ratio are varied. For the investigation of the heat transfer mechanism, the local wall temperatures and heat flux rates were measured at three locations of the cylinder liner in a CFR engine. These fluxes can provide a reliable estimation of the total heat loss through the cylinder walls and of the hydrogen flame arrival at specific locations. Together with the experimental analysis, the numerical results obtained from a validated in-house CFD code were utilized for gaining a more complete view of the heat transfer mechanism and the hydrogen combustion efficiency for the various cases examined. The performance of the CFR engine is then identified, since the calculated cylinder pressures are compared with the measured ones, from which performance and heat release rates are calculated and discussed. Further, NO emission studies have been accomplished, with the calculated results not only being compared with the measured exhaust NO ones, but also further processed for conducting an in-depth investigation of the dependence of NO production on the spatial distribution of in-cylinder gas temperature. It is revealed that for lower fuel/air ratio the burned gas temperature is held at low level and the heat loss ratio is quite low. As the load increases and stoichiometric mixtures are used, the wall and in-cylinder gas temperatures increase substantially, together with the heat loss and the NO emissions, owing to the high hydrogen combustion velocity and the consequent high rate of temperature rise. The combustion efficiency is slightly increased, but the indicated efficiency is decreased due to higher heat loss.