An experimental investigation on hydrogen as a dual fuel for diesel engine system with exhaust gas recirculation technique

With higher rate of depletion of the non-renewable fuels, the quest for an appropriate alternative fuel has gathered great momentum. Though diesel engines are the most trusted power sources in the transportation industry, due to stringent emission norms and rapid depletion of petroleum resources there has been a continuous effort to use alternative fuels. Hydrogen is one of the best alternatives for conventional fuels. Hydrogen has its own benefits and limitations in its use as a conventional fuel in automotive engine system.In the present investigation, hydrogen-enriched air is used as intake charge in a diesel engine adopting exhaust gas recirculation (EGR) technique with hydrogen flow rate at 20 l/min. Experiments are conducted in a single-cylinder, four-stroke, water-cooled, direct-injection diesel engine coupled to an electrical generator. Performance parameters such as specific energy consumption, brake thermal efficiency are determined and emissions such as oxides of nitrogen, hydrocarbon, carbon monoxide, particulate matter, smoke and exhaust gas temperature are measured. Usage of hydrogen in dual fuel mode with EGR technique results in lowered smoke level, particulate and NO_x emissions.     

Effects of exhaust gas recirculation (EGR) on combustion and emissions during cold start of direct injection (DI) diesel engine

Through experiments conducted on a single cylinder direct injection (DI) diesel engine, effects of exhaust gas recirculatoin (EGR) on combustion and emission during cold start were investigated. Combustion of first firing cycle can be promoted significantly by introducing EGR. In experiments, when partially closed choking valve and partially or fully opened EGR valve, peak cylinder pressure of first firing cycle was about 45% higher than that under normal condition without EGR, and the start of combustion (SOC) was also much earlier. EGR also had effects on combustion stability. In the case, which kept 50% or 100% opening of EGR valve (OEV) and kept 100% opening of choking valve (OCV), more stable combustion process was achieved when common rail pressure decreased during cold start. However, excessive amount of EGR led to extreme unstable combustion and even misfiring. Opacity and NO emissions were also analyzed in detail. In the case with maximum EGR, the lowest average opacity, which was less than 4%, was achieved during initial several firing cycles of cold start. But in the later phase, excessive amount of EGR led to a great deal of white smoke emission. NO emission during initial phase of cold start is mainly affected by increase in fuel amount of injection. When combustion became stable gradually, EGR showed significant effect on NO reduction.     

Improving gasoline direct injection (GDI) engine efficiency and emissions with hydrogen from exhaust gas fuel reforming

Exhaust gas fuel reforming has been identified as a thermochemical energy recovery technology with potential to improve gasoline engine efficiency, and thereby reduce CO₂ in addition to other gaseous and particulate matter (PM) emissions. The principle relies on achieving energy recovery from the hot exhaust stream by endothermic catalytic reforming of gasoline and a fraction of the engine exhaust gas. The hydrogen-rich reformate has higher enthalpy than the gasoline fed to the reformer and is recirculated to the intake manifold, i.e. reformed exhaust gas recirculation (REGR).     

Experimental study of engine performance and emissions for hydrogen diesel dual fuel engine with exhaust gas recirculation

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. Hydrogen seems to be a promising alternative fuel for its clean combustion, recyclability and enhanced engine performance. However, problems like high NOx emissions is seen as an exclusive threat to hydrogen fuelled engines. Exhaust gas recirculation (EGR), on the other hand, is known to overcome the aforementioned problem. Therefore, this study is conducted to study the combined effect of hydrogen addition and EGR on the dual fuelled compression ignition engine on a single cylinder diesel engine modified to incorporate manifold hydrogen injection and controlled EGR. The experiments are conducted for 25%, 50%, 75% and 100% loads with the hydrogen energy share (HES) of 0%, 10% and 30%. The EGR rate is controlled between 0%, 5% and 10%. With no substantial decrement in engine's brake thermal efficiency, high gains in terms of emissions are observed due to synergy between hydrogen addition and EGR. The cumulative reduction of 38.4%, 27.4%, 33.4%, 32.3% and 20% with 30% HES and 10% EGR is observed for NOx, CO2, CO, THC and PM, respectively. Hence, the combination of hydrogen addition and EGR is observed to be advantageous for overall emission reduction.     

Effect of exhaust gas recirculation (EGR) temperature for various EGR rates on heavy duty DI diesel engine performance and emissions

DI diesel engines are well established today as the main powertrain solution for trucks and other relevant heavy duty vehicles. At the same time emission legislation (mainly for NO_x and particulate matter) becomes stricter, reducing their limit to extremely low values. One efficient method to control NO_x in order to achieve future emissions limits is the use of rather high exhaust gas recirculation (EGR) rates accompanied by increased boost pressure to avoid the negative impact on soot emissions. The method is based on the reduction of gas temperature level and O₂ availability inside the combustion chamber, but unfortunately it has usually an adverse effect on soot emissions and brake specific fuel consumption (bsfc). The use of high EGR rates creates the need for EGR gas cooling in order to minimize its negative impact on soot emissions especially at high engine load were the EGR flow rate and exhaust temperature are high. For this reason in the present paper it is examined, using a multi-zone combustion model, the effect of cooled EGR gas temperature level for various EGR percentages on performance and emissions of a turbocharged DI heavy duty diesel engine operating at full load. Results reveal that the decrease of EGR gas temperature has a positive effect on bsfc, soot (lower values) while it has only a small positive effect on NO. As revealed, the effect of low EGR temperature is stronger at high EGR rates.     

Control of backfire and NOx emission reduction in a hydrogen fueled multi-cylinder spark ignition engine using cooled EGR and water injection strategies

The experimental study was carried out on a constant speed multi-cylinder spark ignition engine fueled with hydrogen. Exhaust gas recirculation (EGR) and water injection techniques were adopted to control combustion anomalies (backfire and knocking) and reduce NOx emission at source level. The experimental tests were conducted on the engine with varied EGR rate (0%–28% by volume) and water to hydrogen ratio (WHR) (0–9.25) at 15 kW load. It was observed from the experiments that both the strategies can control backfire effectively, but water injection can effectively control backfire compared to EGR. The water injection and EGR reduce the probability of backfire occurrence and its propagation due to the increase in the requirement of minimum ignition energy (MIE) of the charge, caused mainly due to charge dilution effect, and reduction in flame speed respectively. The NOx emission was continuously reduced with increase in EGR rate and WHR, but at higher rates (of EGR and WHR), there was an issue of stability of engine operation. It was found from the experimental results that at 25% EGR, there was 57% reduction in NOx emission without drop in brake thermal efficiency whereas, with WHR of 7.5, the NOx emission was reduced by 97% without affecting the efficiency. The salient point emerging from the study is that water injection technique can control backfire with ultra-low (near zero) NOx emission without compromising the performance of the hydrogen fueled spark ignition engine.     

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.     

Comparison of the effects of EGR and lean burn on an SI engine fueled by hydrogen-enriched low calorific gas

A naturally aspirated spark ignition (SI) engine fueled by hydrogen-blended low calorific gas (LCG) was tested in both exhaust gas recirculation (EGR) and lean burn modes. The “dilution ratio” was introduced to compare their effects on engine performance and emissions under identical levels of dilution. LCG composed of 40% natural gas and 60% nitrogen was used as a main fuel, and hydrogen was blended with the LCG in volumes ranging from 0 to 20%. The engine test results demonstrated that EGR operations at stoichiometry showed a narrower dilution range, inferior combustion characteristics, lower brake thermal efficiency, faster nitrogen oxides (NO_x) suppression, and higher total hydrocarbon (THC) emissions for all hydrogen blending rates compared to lean burn. These trends were mainly due to the increased oxygen deficiency as a result of using EGR in LCG/air mixtures. Hydrogen enrichment of the LCG improved combustion stability and reduced THC emissions while increasing NO_x. In terms of efficiency, hydrogen addition induced a competition between combustion enhancement and increases in the cooling loss, so that the peak thermal efficiency occurred at 10% H₂ with excess air ratio of 1.5. The engine test results also indicated that a close-to-linear NO_x-efficiency relationship occurred for all hydrogen blending rates in both operations as long as stable combustion was achieved. NO_x versus combustion duration analysis showed that adding H₂ reduced combustion duration while maintaining the same level of NO_x. The methane fraction contained in the THC emissions decreased slightly with an increase in hydrogen enrichment at low EGR or excess air dilution ratios, but this tendency was diminished at higher dilution ratios because of the combined dilution effects from the inert gas in the LCG and the diluents (EGR or excess air).     

EGR对双燃料发动机排放特性的影响

废气再循环技术是降低发动机有害排放的有效手段之一。本文介绍了应用于双燃料发动机的废气再循环的装里和实验方法,并详细分析了废气再循环对发动机排放的影响。实验证明朱用废气循环技术降低了发动机的有害排放物。     

废气再循环与燃料辛烷值对均质压燃发动机性能和排放影响的试验研究

在一台单缸直喷式柴油机上研究了废气再循环（EGR）对不同辛烷值燃料均质压燃（HCCI）发动机性能和排放特性的影响。结果表明，混合气较稀，EGR对指示热效率影响较小，其影响和燃料辛烷值有关；混合气变浓，EGR对指示热效率的影响增大。不同辛烷值燃料最高指示热效率出现在高EGR率、混合气较浓的区域，并且靠近爆震燃烧边界，辛烷值为60的燃料最高指示热效率最高，并且覆盖的工况区域最宽。高EGR率区域，EGR对HC排放的影响十分明显，EGR率升高，HC排放急剧增大，而且随着燃料辛烷值增大，这种趋势越明显；CO排放与缸内燃烧温度有较大的相关性，EGR率升高，CO排放升高。NOx排放出现急剧升高的“拐点”是判断HCCI爆震燃烧的一个重要判据，EGR率增大，“拐点”出现的混合气浓度增大，在正常工作范围内，NOx排放极低，EGR对NOx排放几乎没有影响。     

火花点火发动机燃用CNG/H_2混合燃料配合EGR的性能和排放研究

在一台火花点火天然气发动机上开展了不同掺氢比和EGR率下发动机性能和排放的试验研究。研究结果表明:引入EGR后发动机输出功率下降,但掺氢可以提高大EGR工况下发动机的输出功率。有效热效率随EGR率的增大呈现先升高后降低的趋势;小EGR率下,有效热效率随掺氢比的增加而降低,而大EGR率下,有效热效率随掺氢比的增大而升高。天然气掺氢后NOx排放增加,EGR引入使NOx排放降低,这种降低作用在大掺氢比下更显著。因此,相对于小EGR率工况,大EGR率工况下天然气掺氢表现出更好的性能和排放效果。HC排放随EGR率的增大而增加,随掺氢比的增加而降低。CO和CO2都随EGR率的增加变化不大,随掺氢比的增加而降低。研究表明,天然气掺氢结合EGR可实现火花点火发动机高效低污染燃烧,并能满足欧Ⅳ排放标准。     

Effect of manifold and port injection of hydrogen and exhaust gas recirculation (EGR) in dairy scum biodiesel - low energy content gas-fueled CI engine operated on dual fuel mode

In this current work, exhaustive research work is conducted in three phases, in the initial phase, WFO was used for producing WFO treated biomass and in the second phase, influence of PFIP and PFIT has been examined. Further in the successive phase, effect of hydrogen HMI, HPI and EGR on the combustion and emission characteristics of CRDI diesel engine operated on dual-fuel mode using DiSOME and PG combination is evaluated. In the current study, in a CRDI engine, PFIT was employed ranging from 0 to 15°CA bTDC and changed in steps of 5 and PFIP was used from 600 to 1000 bar and varied in successive steps of 200 bar. Further flow rate of hydrogen was kept 8 L/min constant and HMIT was employed in the range from TDC to 15°aTDC and changed in stages of 5. Correspondingly, HID was varied from 30 to 90°CA with 30°CA dwell and EGR was used in the range from 0 to 15% by vol. and varied in steps of 5. Outcome of the work showed that, DiSOME-PG operation with 10°bTDC PFIT, 800 bar PFIP, 10°aTDC of HMI, 60°CAHID and 5% EGR rate showed lower BTE by 5.8% and increased smoke levels by 10.8%, HC by 8.6%, CO by 6.5% and marginally decreased NOx by 6.4% was observed in comparison to the same fuel blend with zero EGR at 80% load. Further, marginally amplifiedID and CD with loweredCP and HRR has been noticed. Study revealed thatH₂addition to low calorific value gas (PG), method of pilot fuel addition and EGR is affected dual fuel engine performance, but provided drastic reductions in smoke and NOx emissions.     

废气再循环与燃料辛烷值对均质压燃燃烧特性影响的试验研究

在一台单缸直喷式柴油机上研究了废气再循环（EGR）对不同辛烷值燃料均质压燃（HCCI）燃烧特性及排放特性的影响.结果表明,EGR使HCCI着火燃烧推迟、燃烧反应速度降低、缸内压力和平均温度降低,HCCI工况范围向大负荷工况扩展;混合气浓度增大或燃料辛烷值增大,EGR对燃烧效率的影响增大,EGR率升高,燃烧效率降低;不同辛烷值燃料最高燃烧效率出现在高比例EGR率、混合气较浓、靠近爆震燃烧边界的区域.试验结果也表明,辛烷值为60的燃料采用EGR后HCCI覆盖的工况范围最宽.     

废气再循环对二甲基醚均质压燃燃烧过程影响的试验研究

在一台单缸发动机上进行了废气再循环(EGR)对二甲基醚(DME)均质压燃(HCCI)燃烧过程影响的试验研究。结果表明，EGR比例小于20％对运行最大负荷工况范围影响不大；采用高比例EGR可以拓宽DME均质压燃运行工况范围，随着EGR率增大，HCCI运行的最大负荷工况增大，着火燃烧时刻推迟，燃烧放热率降低，缸内最大爆发压力降低，发动机热效率增大；EGR率小于75％，HC排放略有降低或相当，EGR率为75％时，HC排放显著增加；EGR率大于25％，随着EGR率增加，CO排放增大，小负荷工况尤其明显，在中高负荷工况，EGR率对CO排放影响较小。     

Investigation on the effect of injection schedule and EGR in hydrogen energy share using common rail direct injection dual fuel engine

In this research work, four different diesel injection schedules have been experimented at a BMEP of 2 bar (Low load) in hydrogen diesel dual fuel (HDDF) mode, which are namely single pulse, double pulse phase-1, double pulse phase-2 and multi-pulse. The maximum possible hydrogen energy shares (HES) for single pulse, double pulse phase-1, double pulse phase-2 and multi-pulse injection schedules were 73.99%, 48.98%, 34.46% and 24.39% respectively. Over the injection schedules, double pulse phase-2 improved the brake thermal efficiency (BTE) from 19.50% (single pulse) to 21.61% with a penalty in NO emission. On the other hand, multi-pulse moderately increased the BTE with significant reduction in NO beside rise in smoke emission. At a BMEP of 5 bar (Medium load) operation, there was a considerable reduction in NO emission at maximum range of HES level with 18.21% of EGR, moreover the engine stability was improved with minor increase in smoke emission.     

Hydrogen rich exhaust gas recirculation (H2EGR) for performance improvement and emissions reduction of a compression ignition engine

Hydrogen (H₂), being carbon free energy carrier, is best suitable for compression ignition (CI) engines with better performance and lower carbon derived emissions. Novelty of present study is the employment of low-cost catalyst (alumina) for production of H₂ reformate (hydrogen rich exhaust gas recirculation: H2EGR) in an indigenous catalytic reactor. Experimental tests were carried out on a CI engine under three conditions; base diesel, exhaust gas recirculation (EGR), and H2EGR. Results indicated that brake thermal efficiency of the engine with H2EGR was higher than EGR and comparable with base diesel operation. All carbon-based emissions including smoke emission decreased significantly with H2EGR than diesel and EGR operations. In addition, oxides of nitrogen emission (NO_x) also decreased by about 46% with H2EGR than base diesel operation. It is concluded that H2EGR is a promising option for CI engines for simultaneous reduction of both NO_x and smoke emissions along with the additional benefit of higher efficiency.     

Experimental study of various effects of exhaust gas recirculation (EGR) on combustion and emissions of an automotive direct injection diesel engine

Cooled exhaust gas recirculation (EGR) is a common way to control in-cylinder NO_x production and is used on most modern high-speed direct injection (HSDI) diesel engines. However EGR has different effects on combustion and emissions production that are difficult to distinguish (increase of intake temperature, delay of rate of heat release (ROHR), decrease of peak heat release, decrease in O₂ concentration (and thus of global air/fuel ratio (AFR)) and flame temperature, increase of lift-off length, etc.), and thus the influence of EGR on NO_x and particulate matter (PM) emissions is not perfectly understood, especially under high EGR rates. An experimental study has been conducted on a 2.0 l HSDI automotive diesel engine under low-load and part load conditions in order to distinguish and quantify some effects of EGR on combustion and NO_x/PM emissions. The increase of inlet temperature with EGR has contrary effects on combustion and emissions, thus sometimes giving opposite tendencies as traditionally observed, as, for example, the reduction of NO_x emissions with increased inlet temperature. For a purely diffusion combustion the ROHR is unchanged when the AFR is maintained when changing in-cylinder ambient gas properties (temperature or EGR rate). At low-load conditions, use of high EGR rates at constant boost pressure is a way to drastically reduce NO_x and PM emissions but with an increase of brake-specific fuel consumption (BSFC) and other emissions (CO and hydrocarbon), whereas EGR at constant AFR may drastically reduce NO_x emissions without important penalty on BSFC and soot emissions but is limited by the turbocharging system.     

EGR对直喷式柴油机冷起动过程着火燃烧的影响分析

通过在一台135单缸直喷柴油机上分别进行内部EGR（IEGR）、外部EGR（EEGR）条件下的冷起动试验,分析了内、外部EGR对柴油机冷起动过程着火燃烧性能及排放的影响。加入内、外部EGR后,由于EGR中含有大量的燃油蒸气、部分氧化产物等活性成分,初始着火循环的着火燃烧性能得到显著改善。在冷起动过程中,加入一定量的内部或外部EGR,有利于提高燃烧过程的稳定性。但过大的外部EGR量,将导致发动机燃烧极度不稳定甚至失火。由试验结果还可以看到,加入适当的内、外部EGR,均能有效地改善冷起动过程的烟度排放。对于NOx排放,当采用外部EGR方式时,有明显的改善作用;但当采用内部EGR方式时,由于残余废气的热效应,NOx排放随内部EGR量的增大而增大。     

Combustion and emission characteristics of an Acetone-Butanol-Ethanol (ABE) spark ignition engine with hydrogen direct injection

Butanol could reduce emissions and alleviate the energy crisis as a bio-fuel used on engines, but the production cost problem limits the application of butanol. During the butanol production, ABE (Acetone-Butanol-Ethanol) is a critical intermediate product. Many studies researched the direct application of ABE on engines instead of butanol to solve the production cost problem of butanol. ABE has the defects of large ignition energy and vaporization heat. Hydrogen is a gaseous fuel with small ignition energy and high flame temperature. In this research, ABE port injection combines with hydrogen direct injection, forming a stratified state of the hydrogen-rich mixture around the spark plug. The engine speed is 1500 rpm, and λ is 1. Five αH₂ (hydrogen blending fractions: 0, 5%, 10%, 15%, 20%) and five spark timings (5°, 10°, 15°, 20°, 25° CA BTDC) are studied to observe the effects of them on combustion and emissions of the test engine. The results show that hydrogen addition increases the maximum cylinder pressure and maximum heat release rate, increases the maximum cylinder temperature and IMEP, but the exhaust temperature decreases. The flame development period and flame propagation period shorten after adding hydrogen. Hydrogen addition improves HC and CO emissions but increases NO_x emissions. Particle emissions decrease distinctly after hydrogen addition. Hydrogen changes the combustion properties of ABE and improves the test engine's power and emissions. The combustion in the cylinder becomes better with the increase of αH₂, but a further increase in αH₂ beyond 5% brings minor improvements on combustion.