Performance and emission characteristics of CIE using hydrogen,biodiesel, and massive EGR

Hydrogen is considered as an excellent energy carrier and can be used in diesel engines that operate in dual fuel mode. Many studies have shown that biodiesel, which is sustainable, clean, and safe, a good alternative to fossil fuel. However, tests have confirmed that using biodiesel or hydrogen as a fuel or added fuel in compression ignition engines increases NOx concentrations. Cooled or hot exhaust gas recirculation (EGR) effectively controls the NOx outflows of diesel engines. However, this technique is restricted by high particulate matter PM emissions and the low thermal efficiency of diesel engines.In this study, gaseous hydrogen was added to the intake manifold of a diesel engine that uses biodiesel fuel as pilot fuel. The investigation was conducted under heavy-EGR conditions. An EGR system was modified to achieve the highest possible control on the EGR ratio and temperature. Hot EGR was recirculated directly from the engine exhaust to the intake manifold. A heat exchanger was utilized to maintain the temperature of the cooled EGR at 25 °C.The supplied hydrogen increased NOx concentrations in the exhaust gas emissions and high EGR rates reduced the brake thermal efficiency. The reduction in NOx emissions depended on the added hydrogen and the EGR ratios when compared with pure diesel combustion. Adding hydrogen to significant amounts of recycled exhaust gas reduced the CO, PM, and unburned hydrocarbon (HC) emissions significantly. Results showed that using hydrogen and biodiesel increases engine noise, which is reduced by adding high levels of EGR.     

Hydrogen effects on NOx emissions and brake thermal efficiency in a diesel engine under low-temperature and heavy-EGR conditions

Cooled and heavy exhaust gas recirculation (EGR) has been used to control NOx emissions from diesel engines, but its application has been limited by low thermal efficiency or high unburned hydrocarbon emissions. In this study, hydrogen was added into the intake manifold of a diesel engine to investigate its effect on NOx emissions and thermal efficiency under low-temperature and heavy-EGR conditions. The energy content of the introduced hydrogen was varied from an equivalent of 2-10% of the total fuel’s lower heating value. A test engine was operated at a constant diesel fuel injection rate and engine speed to maintain the same engine control unit (ECU) parameters, such as injection time, while observing changes in the carbon dioxide produced due to variations in the hydrogen supply. Additionally, the EGR system was modified to control the EGR ratio. The temperature of the intake gas manifold was controlled by both the EGR cooler and the inter-cooling devices to maintain a temperature of 25 °C. Exhaust NOx emissions were measured for different hydrogen flow rates at a constant EGR ratio. The test results demonstrated that the supplied hydrogen reduced the specific NOx emissions at a given EGR ratio while increasing the brake thermal efficiency. This behavior was observed over constant EGR ratios of 2, 16, and 31%. The rate of NOx reduction due to hydrogen addition increased at higher EGR ratios compared with pure diesel combustion at the same EGR ratio. At an EGR ratio of 31%, when the hydrogen equivalent to 10% of the total fuel’s lower heating value was supplied, the specific NOx was lowered by 25%, and there was a slight increase in the brake thermal efficiency. This behavior was investigated by measuring and analyzing changes in the exhaust gas composition, including oxygen, carbon dioxide, and water vapor.     

降低小型柴油机排放的试验研究

从生物混合燃料成分、燃烧室结构和排气再循环等方面探索降低柴油机排放的方法。通过对柴油机排放性能的大量试验研究,结果表明:对于直喷式柴油机,生物混合燃料的NOx排放与柴油的排放基本相当,碳烟排放则比柴油有较大幅度的降低,而涡流室柴油机,NOx的排放量却有大幅度的降低,碳烟排放则比直喷式柴油机有更大幅度的降低,生物燃料的添加比例对NOx的排放影响不大。柴油机采用排气再循环技术后,混合燃料的碳烟排放仍比柴油少,混合燃料可以承载一定的EGR率而不增加碳烟排放。排气再循环可以大幅度地降低NOx排放且与EGR率有关,与燃料的性质关系不大。涡流室柴油机采用生物燃料和排气再循环,可以同时降低NOx和碳烟的排放,排放效果非常优良。     

Effect of hydrogen on compression-ignition (CI) engine fueled with vegetable oil/biodiesel from various feedstocks: A review

Compression ignition (CI) engines used in the transportation sector operates on fossil diesel and is one of the biggest causes of air pollution. Numerous studies were carried out over last two decades to substitute the fossil diesel with biofuels so that the net carbon dioxide (CO₂) emission can be minimized. However, the engine performance with these fuel was sub-standard and there were many long-term issues. Therefore, many researchers inducted hydrogen along with the biofuels. The present study gives an outlook on the effect of hydrogen addition with biodiesel/vegetable oil from various sources in CI engine. Engine parameters (brake thermal efficiency, brake specific fuel consumption), combustion parameters (in-cylinder pressure and heat release rate) and emission parameters (unburned hydrocarbon (HC), carbon monoxide (CO), oxides of nitrogen (NOx) and smoke emissions) were evaluated in detail. The results show that hydrogen induction in general improves the engine performance as compared to biodiesel/vegetable oil but it is similar/lower than diesel. Except NOx emissions all other emissions showed a decreasing trend with hydrogen addition. To counter this effect numerous after-treatment systems like selective catalytic reduction (SCR), exhaust gas recirculation (EGR), selective non-catalytic reduction system (SNCR) and non-selective catalytic reduction system (NSCR) were proposed by researchers which were also studied in this review.     

Use of HOT EGR for NOx control in a compression ignition engine fuelled with bio-diesel from Jatropha oil

Environmental degradation and depleting oil reserves are matters of great concern round the globe. Developing countries like India depend heavily on oil import. Diesel being the main transport fuel in India, finding a suitable alternative to diesel is an urgent need. Jatropha based bio-diesel (JBD) is a non-edible, renewable fuel suitable for diesel engines and is receiving increasing attention in India because of its potential to generate large-scale employment and relatively low environmental degradation. Diesel engines running on JBD are found to emit higher oxides of nitrogen, NO_x. HOT EGR, a low cost technique of exhaust gas recirculation, is effectively used in this work to overcome this environmental penalty. Practical problems faced while using a COOLED EGR system are avoided with HOT EGR. Results indicated higher nitric oxide (NO) emissions when a single cylinder diesel engine was fuelled with JBD, without EGR. NO emissions were reduced when the engine was operated under HOT EGR levels of 5–25%. However, EGR level was optimized as 15% based on adequate reduction in NO emissions, minimum possible smoke, CO, HC emissions and reasonable brake thermal efficiency. Smoke emissions of JBD in the higher load region were lower than diesel, irrespective of the EGR levels. However, smoke emission was higher in the lower load region. CO and HC emissions were found to be lower for JBD irrespective of EGR levels. Combustion parameters were found to be comparable for both fuels.     

Effect of addition of hydrogen and exhaust gas recirculation on characteristics of hydrogen gasoline engine

The effects of exhaust gas recirculation (EGR) on combustion and emissions under different hydrogen ratios were studied based on an engine with a gasoline intake port injection and hydrogen direct injection. The peak cylinder pressure increases by 9.8% in the presence of a small amount of hydrogen. The heat release from combustion is more concentrated, and the engine torque can increase by 11% with a small amount of hydrogen addition. Nitrogen oxide (NOx) emissions can be reduced by EGR dilution. Hydrogen addition offsets the blocking effect of EGR on combustion partially, therefore, hydrogen addition permits a higher original engine EGR rate, and yields a larger throttle opening, which improves the mechanical efficiency and decreases NOx emissions by 54.8% compared with the original engine. The effects of EGR on carbon monoxide (CO) and hydrocarbon (HC) emissions are not obvious and CO and HC emissions can be reduced sharply with hydrogen addition. CO, HC, and NOx emissions can be controlled at a lower level, engine output torque can be increased, and fuel consumption can be reduced significantly with the co-control of hydrogen addition and EGR in a hydrogen gasoline engine.     

A review of hydrogen as a compression ignition engine fuel

Diesel fuelled engines emit higher levels of carbon dioxide and other harmful air pollutants (such as noxious gases and particulates) per litre of fuel than gasoline engines. This fact, combined with the recent diesel emission scandal and the rumours of more widespread cheating by automotive manufacturers have initiated a long discussion about the future and sustainability of diesel engines.Improving the compression ignition engine is a direct way of going green. Reducing the harmful emissions can be achieved by future developments in the engine technology but also the implementation of alternative fuels. Hydrogen is a renewable, high-efficient and clean fuel that can potentially save the future of diesel-type engines. The evolution of high-efficiency renewable hydrogen production methods is the most important path for the start of a new hydrogen era for the compression ignition engine that can improve its sustainability and maximum efficiency.This paper provides a detailed overview of hydrogen as a fuel for compression ignition engines. A comprehensive review of the past and recent research activities on the topic is documented. The review focuses on the in-cylinder combustion of hydrogen either as a primary fuel or in dual fuel operation. The effects of injection strategies, compression ratio and exhaust gas recirculation on the combustion and emission characteristics of the hydrogen fuelled engine are fully analysed. The main limitations, challenges and perspectives are presented.     

Engine combustion and emission fuelled with natural gas: A review

Natural gas (NG) is one of the most important and successful alternative fuels for vehicles. Engine combustion and emission fuelled with natural gas have been reviewed by NG/gasoline bi-fuel engine, pure NG engine, NG/diesel dual fuel engine and HCNG engine. Compared to using gasoline, bi-fuel engine using NG exhibits higher thermal efficiency; produces lower HC, CO and PM emissions and higher NOx emission. The bi-fuel mode can not fully exert the advantages of NG. Optimization of structure design for engine chamber, injection parameters including injection timing, injection pressure and multi injection, and lean burn provides a technological route to achieve high efficiency, low emissions and balance between HC and NOx. Compared to diesel, NG/diesel dual fuel engine exhibits longer ignition delay; has lower thermal efficiency at low and partial loads and higher at medium and high loads; emits higher HC and CO emissions and lower PM and NOx emissions. The addition of hydrogen can further improve the thermal efficiency and decrease the HC, CO and PM emissions of NG engine, while significantly increase the NOx emission. In each mode, methane is the major composition of THC emission and it has great warming potential. Methane emission can be decreased by hydrogen addition and after-treatment technology.     

Numerical investigation on hydrogen-diesel dual-fuel engine improvements by oxygen enrichment

Hydrogen-diesel dual fuel (HDDF) technology is one approach available to improve the performance and reduce carbon-based emissions of compression ignition (CI) engines. Unfortunately, when operated at partial and low loads, HDDF engine configurations suffer from poor fuel utilization, combustion efficiency and ignition delay. As partial load application is increasingly important to performance of hybrid power systems, this paper explores the use of oxygen enrichment to improve HDDF performance outside of conventional load applications.In this paper, a numerical model was first developed and validated for HDDF combustion using experimental data. This model was subsequently applied to study the influences of oxygen enrichment on engine performance and emission characteristics. Furthermore, the Exhaust Gas Recirculation (EGR) was implemented as a secondary control for NOx emission reduction. For this configuration the results showed that oxygen enrichment (between 21% and 27% by volume) into the intake manifold led to an improved combustion efficiency and reduced carbon-based emissions. The brake thermal efficiency (BTE) increased by 1.6% and the brake specific energy consumption decreased by 4%. Across the emissions spectrum, soot emission reduced by 72%, whereas NOx emission increased by 63% without using the EGR technique. By combining oxygen enrichment and EGR strategies, a considerable reduction of 79% in NOx and an increase of 2.6% in BTE was observed for the oxygen concentration of 27% and EGR rate of 24% compared to a conventional HDDF operation with 45% HES ratio.     

Effect of hydrogen supplementation on engine performance and emissions

Vehicular Pollution and environmental degradation are on the rise with increasing vehicles and to stop this strict regulation have been put on vehicular emissions. Also, the depleting fossil fuels are of great concern for energy security. This has motivated the researchers to invest considerable resources in finding cleaner burning, sustainable and renewable fuels. However renewable fuels independently are not sufficient to deal with the problem at hand due to supply constraints. Hence, advanced combustion technologies such as homogeneous charge compression ignition (HCCI), low-temperature combustion (LTC), and dual fuel engines are extensively researched upon. In this context, this work investigates dual fuel mode combustion using a constant speed diesel engine, operated using hydrogen and diesel. The engine is operated at 25, 50 and 75% loads and substitution of diesel energy with hydrogen energy is done as 0, 5, 10 and 20%. The effect of hydrogen energy share (HES) enhancement on engine performance and emissions is investigated. In the tested range, slightly detrimental effect of HES on brake thermal efficiency (BTE) and brake specific fuel consumption (BSFC) is observed. Comparision of NO and NO₂ emissions is done to understand the non-thermal influence of H₂ on the NO_x emissions. Hence, HES is found beneficial in reducing harmful emissions at low and mid loads.     

Hydrogen effects on the diesel engine performance and emissions

In this research, effects of hydrogen addition on a diesel engine were investigated in terms of engine performance and emissions for four cylinders, water cooled diesel engine. Hydrogen was added through the intake port of the diesel engine. Hydrogen effects on the diesel engine were investigated with different amount (0.20, 0.40, 0.60 and 0.80 lpm) at different engine load (20%, 40%, 60%, 80% and 100% load) and the constant speed, 1800 rpm. When hydrogen amount is increased for all engine loads, it is observed an increase in brake specific fuel consumption and brake thermal efficiency due to mixture formation and higher flame speed of hydrogen gas according to the results. For the 0.80 lpm hydrogen addition, exhaust temperature and NOx increased at higher loads. CO, UHC and SOOT emissions significantly decreased for hydrogen gas as additional fuel at all loads. In this study, higher decrease on SOOT emissions (up to 0.80lpm) was obtained. In addition, for 0.80 lpm hydrogen addition, the dramatic increase in NOx emissions was observed.     

Statistical and experimental investigation of the influence of fuel injection strategies on CRDI engine assisted CNG dual fuel diesel engine

With an alarming enlargement in vehicular density, there is a threat to the environment due to toxic emissions and depleting fossil fuel reserves across the globe. This has led to the perpetual exploration of clean energy resources to establish sustainable transportation. Researchers are continuously looking for the fuels with clean emission without compromising much on vehicular performance characteristics which has already been set by efficient diesel engines. In this study, the combustion, performance and emission characteristics of CRDI diesel engine assisted CNG dual fuel research engine operated at constant speed of 1500 rpm with variable engine load (16, 20 and 24 NM) to analyses the influence of fuel injection timings (7.5, 12.5 and 17.5 SOI) and fuel injection pressure (500, 750 and 1000 bar) under reactivity-controlled compression ignition (RCCI) mode. In the case of a fuel injection pressure of 1000 bar, the maximum brake specific fuel consumption of 0.42 kg/kWh is registered with a brake mean effective pressure of 3.2 bar. Response surface methodology has been used in this analysis for predicting the optimal input parameters (engine load, fuel injection timing, and fuel injection pressure), which results in an optimal combination of performance (BP, BTHE, and BSFC) and emission (HC, NOx, and CO) parameters. A variety of optimal solutions based on the desirability method is obtained from the model, and optimal input parameters is suggested as load 20(Nm), injection pressure 750(Bar), and injection timing (BTDC) 12.5. Additionally, to obtain a ‘regression model’ a statistically significant test (ANOVA) is developed. Results have shown that the suggested ‘Regression Model’ is best fitted to 0.095 standard deviations, 0.972 corrected R², and 18.482 acceptable accuracy.     

Emission and engine performance analysis of a diesel engine using hydrogen enriched pomegranate seed oil biodiesel

The aim of this study is to determine the availability of pomegranate seed oil biodiesel (POB) as an alternative fuel in diesel engines and evaluate engine performance and emission characteristics of pure hydrogen enriched POB using diesel engine. For this purpose, the intake manifold of the test engine was modified and hydrogen enriched intake air was supplied throughout the experiments. Physical properties of POB and its blend with diesel fuel were also determined. The results showed that measured physical properties of POB are comparable with diesel fuel. According to engine performance experiments, although POB utilization has slight undesirable effects on some engine performance parameters such as brake power output and specific fuel consumption, it can be used as alternative fuel in diesel engines, by this way CO emission can be improved. Finally, hydrogen enrichment experiments indicated that pure hydrogen addition causes a slight improvement in both engine performance and exhaust emissions.     

Effect of exhaust gas recirculation on diesel engine nitrogen oxide reduction operating with jojoba methyl ester

Jojoba methyl ester (JME) has been used as a renewable fuel in numerous studies evaluating its potential use in diesel engines. These studies showed that this fuel is good gas oil substitute but an increase in the nitrogenous oxides emissions was observed at all operating conditions. The aim of this study mainly was to quantify the efficiency of exhaust gas recirculation (EGR) when using JME fuel in a fully instrumented, two-cylinder, naturally aspirated, four-stroke direct injection diesel engine. The tests were carried out in three sections. Firstly, the measured performance and exhaust emissions of the diesel engine operating with diesel fuel and JME at various speeds under full load are determined and compared. Secondly, tests were performed at constant speed with two loads to investigate the EGR effect on engine performance and exhaust emissions including nitrogenous oxides (NO_x), carbon monoxide (CO), unburned hydrocarbons (HC) and exhaust gas temperatures. Thirdly, the effect of cooled EGR with high ratio at full load on engine performance and emissions was examined. The results showed that EGR is an effective technique for reducing NO_x emissions with JME fuel especially in light-duty diesel engines. With the application of the EGR method, the CO and HC concentration in the engine-out emissions increased. For all operating conditions, a better trade-off between HC, CO and NO_x emissions can be attained within a limited EGR rate of 5–15% with very little economy penalty.     

Effect of induction on exhaust gas recirculation and hydrogen gas in compression ignition engine with simarouba oil in dual fuel mode

Biofuels extracted from non-edible oil is sustainable and can be used as an alternative fuel for internal combustion engines. This study presents the performance, emission and combustion characteristic analysis by using simarouba oil (obtained from Simarouba seed) as an alternative fuel along with hydrogen and exhaust gas recirculation (EGR) in a compression ignition (CI) engine operating on dual fuel mode. Simarouba biofuel blend (B20) was prepared on volumetric basis by mixing simarouba oil and diesel in the proportion of 20% and 80% (v/v), respectively. Hydrogen gas was introduced at the flow rate of 2.67 kg/min, and EGR concentration was maintained at 30% of total air introduction. Performance, combustion and emission characteristics analysis were examined with biodiesel (B20), biodiesel with hydrogen substitution and biodiesel, hydrogen with EGR and were compared with neat diesel operation. Results indicate that BTE of the engine operating with biodiesel B20 was decreased when compared to neat diesel operation. However, introducing hydrogen along with B20 blend into the combustion chamber shows a slight increase in the BTE by 1%. NO_x emission was increased to 18.13% with the introduction of hydrogen than that of base fuel (diesel) operation. With the introduction of EGR, there is a significant reduction in NO_x emission due to decrease in in-cylinder temperature by 19.07%. A significant reduction in CO, CO_2, and smoke emissions were also noted with the introduction of both hydrogen and EGR. The ignition delay and combustion duration were increased with the introduction of hydrogen, EGR with biodiesel than neat diesel operation. Hence, the proposed biodiesel B20 with H₂ and EGR combination can be applied as an alternative fuel in CI engines.     

Effect of Exhaust Gas Recirculation (EGR) on performance,emissions, deposits and durability of a constant speed compression ignition engine

To meet stringent vehicular exhaust emission norms worldwide, several exhaust pre-treatment and post-treatment techniques have been employed in modern engines. Exhaust Gas Recirculation (EGR) is a pre-treatment technique, which is being used widely to reduce and control the oxides of nitrogen (NO_x) emission from diesel engines. EGR controls the NO_x because it lowers oxygen concentration and flame temperature of the working fluid in the combustion chamber. However, the use of EGR leads to a trade-off in terms of soot emissions. Higher soot generated by EGR leads to long-term usage problems inside the engines such as higher carbon deposits, lubricating oil degradation and enhanced engine wear. Present experimental study has been carried out to investigate the effect of EGR on soot deposits, and wear of vital engine parts, especially piston rings, apart from performance and emissions in a two cylinder, air cooled, constant speed direct injection diesel engine, which is typically used in agricultural farm machinery and decentralized captive power generation. Such engines are normally not operated with EGR. The experiments were carried out to experimentally evaluate the performance and emissions for different EGR rates of the engine. Emissions of hydrocarbons (HC), NO_x, carbon monoxide (CO), exhaust gas temperature, and smoke opacity of the exhaust gas etc. were measured. Performance parameters such as thermal efficiency, brake specific fuel consumption (BSFC) were calculated. Reduction in NO_x and exhaust gas temperature were observed but emissions of particulate matter (PM), HC, and CO were found to have increased with usage of EGR. The engine was operated for 96 h in normal running conditions and the deposits on vital engine parts were assessed. The engine was again operated for 96 h with EGR and similar observations were recorded. Higher carbon deposits were observed on the engine parts operating with EGR. Higher wear of piston rings was also observed for engine operated with EGR.     

Separate and combined effects of hydrogen and nitrogen additions on diesel engine combustion

Shortage of non-renewable energies, increase in fossil fuel prices and stricter emissions regulations due to high NOx and soot emissions emitted from combustion of heavy diesel fuels by compression ignition engines, has led consumers to use renewable, cleaner and cheap fuels. An investigation has been computationally carried out to explore the influences of hydrogen and nitrogen addition on engine performance such as indicated power and indicated specific energy consumption and amounts of pollutant emissions like NOx, soot, and CO in an HSDI (High-Speed Direct Injection) diesel engine. Optimized sub-models, such as turbulence model, spray model, combustion model and emissions models have selected for the main CFD code. Meanwhile, HF (Homogeneity Factor) has been employed for analysing in-cylinder air-fuel mixing quality under various addition conditions. After validations with experimental data of diesel combustion with a single addition of 4% hydrogen and combined addition of 6% hydrogen + 6% nitrogen, investigations have conducted for modeling mixing and combustion processes with additions of hydrogen and nitrogen by ranges of 2–8% (v/v). Results showed that a single addition of H₂ increased NOx and decreased CO and soot and improved ISEC and IP. In the case of nitrogen addition, NOx decreased, both CO and soot emission increased and ISEC and IP considerably ruined compared with NDC operation. Based on the results obtained for simultaneous addition of N₂ (8% of v/v) and H₂ (8% of v/v), NOx and soot emissions decreased by 11.5% and 42.5% respectively, and ISEC and IP improved 25.7% and 13%, respectively. But amount of CO emissions had an increase of 52% should be paid necessary attention as a main disadvantage.     

Simulation of diesel hybrid electric vehicle containing hydrogen enriched CI engine

Hydrogen enrichment on diesel engines is a proven solution for both minimizing the undesirable emissions and fuel consumptions. Also, hybrid electric vehicles which manufactured for the same goal too, are playing an important movement during three decades in transportation sector. The combination of these two common-purpose technologies will give possibility to production of hybrid electric vehicles which have hydrogen-enriched internal combustion engine, in the near future.At this study, four type modelled vehicle; stock diesel vehicle (V1), hydrogen enrichment diesel vehicle (V2), hybrid electric vehicle which contains same diesel engine (V3) and hybrid electric vehicle that powered by hydrogen enrichment diesel engine (V4); simulated with AVL simulation tools for compared the performance and emission values, for the first time. V1 is outfitted by 3.0 L diesel engine. V2 is the hydrogen enriched version of V1 which hydrogen addition is conducted via intake manifold with 8% (vol/vol) enrichment. V1 and V2 were simulated under AVL Boost tool for analyzing the effects of hydrogen addition clearly. After that, V3 and V4 were modelled with AVL Cruise. V3 and V4 were coupled an electric motor (30 kW) with appropriate battery. In terms of performance and emissions results, vehicle types with hydrogen enriched diesel engines were given promising outputs when compared with without ones. In particular, V4 has revealing excellent performance. Under this study's circumstances, when compared V4 between stock one, 4.26% improvement was achieving on vehicle performance parameters. Additionally, the combined fuel consumption, NOx emission and CO2 emission decreases with 14.32%, 15% and 33% respectively, for comparison between V4 and V1.     

Reduction of emissions in a biodiesel‐fueled compression ignition engine using exhaust gas recirculation and selective catalytic reduction techniques

This paper analyzes the emissions of a single‐cylinder diesel engine fueled with biodiesel, using selective catalytic reduction (SCR) and exhaust gas recirculation (EGR) techniques. The aim of this paper is to compare both EGR and SCR techniques, which were studied under different brake powers. Grape seed biodiesel was used as a test fuel. Experiments were performed by both techniques at different loads and rates to find out the performance change in the engine and the change in the emission rates using both the techniques. Then the observations from both the techniques were compared, concluding that both the techniques show a sufficient reduction in NOx. Using the abovementioned techniques, a reduction in hydrocarbon (HC), carbon monoxide (CO), carbon dioxide (CO₂), nitrogen oxides (NOx), and smoke was observed. The EGR technique is more suitable for low‐load engine vehicles, as it affects the efficiency of the engine with an increase in the fuel consumption, whereas the SCR technique is suitable for high‐load engines, which do not affect the efficiency of the engine with a decrease in the fuel consumption.     

The effect of EGR and hydrogen addition to natural gas on performance and exhaust emissions in a diesel engine by AVL fire multi-domain simulation,GPR model,and multi-objective genetic algorithm

In this study, the effect of adding hydrogen to natural gas and EGR ratio was conducted on a diesel engine to investigate the engine performance and exhaust gases by AVL Fire multi-domain simulation software.For this investigation, a mixture of hydrogen fuel and natural gas replaced diesel fuel. The percentage of hydrogen in blend fuel changed from 0% to 40%. The compression ratio converted from 17:1 to 15:1. The EGR ratios were in three steps of 5%, 10%, and 15%, with different engine speeds from 1000 to 1800 RPM. The Gaussian process regression (GPR) was developed to model engine performance and exhaust emissions. The optimal values of EGR and the percentage of hydrogen in the blend of HCNG were extracted using a multi-objective genetic algorithm (MOGA).The results showed that by increasing EGR, thermal efficiency, the engine power, and specific fuel consumption decreased due to prolongation of combustion length while cumulative heat release increased but, its effect on cylinder pressure is insignificant. Adding hydrogen to natural gas increased the combustion temperature and, consequently NOx. While the amount of CO and HC decreased. The results of GPR and MOGA illustrated that at different engine speeds, the optimum values of EGR and HCNG were 6.35% and 31%, respectively.