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.     

Hydrogen applications in selective catalytic reduction of NOx emissions from diesel engines

Diesel engines have been considered as a major source in nitrogen oxide (NO_x) formation worldwide. The widespread use of diesel engines in consequence of their low fuel consumption, high durability and efficiency increases NO_x emissions day by day. NO_x emissions from diesel engines cause unavoidable damage on environment and people health. Although so many technologies such as exhaust gas recirculation (EGR), lean burn combustion, electronic controlling fuel injection systems, etc. have been developed to control NO_x emissions from diesel engines, they couldn't meet the desired reduction in NO_x emissions. In any case, Selective Catalytic Reduction (SCR) as one of the most promising aftertreatment-emission control technologies is an effective solution in restriction of NO_x emissions. The use of SCR systems especially in heavy-duty diesel powered vehicles has been increasing nowadays. In these systems, to use of hydrogen (H₂) as a reductant or promoter have been improved the conversion efficiency especially at low exhaust temperatures. Many researchers have been focused on the use of H₂ in SCR systems for controlling NO_x emissions.In this study, the applications of H₂ in SCR of NO_x have been discussed. The studies on use of H₂ in SCR of NO_x emissions were examined and the effects on NO_x conversions were determined. Consequently, it is confirmed that H₂ is a promising and alternative reductant in SCR of NO_x and it has been kept as an attracting subject for many researchers.     

The effect of HRG gas addition on diesel engine combustion characteristics and exhaust emissions

Extensive studies have been dedicated in the last decade to the possibility to use hydrogen in the dual-fuel mode to improve combustion characteristics and emissions of a diesel engine. The results of these studies, using pure hydrogen or hydrogen containing gas produced through water electrolysis, are notably different.The present investigation was conducted on a tractor diesel engine running with small amounts of the gas—provided by a water electrolyzer—aspirated in the air stream inducted in the cylinder. The engine was operated at light and medium loads and various speeds.It was found that the addition of HRG gas has a slight negative impact, up to 2%, on the engine brake thermal efficiency. Smoke is significantly reduced, up to 30%, with HRG enrichment, while NO_x concentrations vary in both senses, up to 14%, depending on the engine operation mode. A relative small amount of HRG gas can be used with favorable effects on emissions and with a small penalty in thermal efficiency.     

Efficiency and emissions in a vehicle spark ignition engine fueled with hydrogen and methane blends

This paper shows the results of the tests carried out in a naturally aspirated vehicle spark ignition engine fueled with different hydrogen and methane blends. The percentage of hydrogen tested was up to 50% by volume in methane. The tests were carried out in a wide range of speeds with the original ignition timing of the engine. Also, lean equivalence ratios were proved. Just the fuel injection map was modified for each fuel blend and equivalence ratio tested. In this paper, the results of thermal efficiency and pollutant emissions achieved at full load have been compared with the corresponding gasoline test results. The best balance between thermal efficiency and pollutant emissions was observed with the 30% hydrogen and 70% methane fuel blend.     

The effects of hydrogen enriched natural gas under different engine loads in a diesel engine

Natural gas, which is among the alternative fuels, has become widespread in the transportation as it is both economical and environmentally friendly. While the use of natural gas is at a significant level in spark ignition engines, it has not yet been implemented in compression ignition engines (CI) as it worsens combustion due to ignition delay. In CI engines, however, the combustion properties of natural gas (NG) can be improved by adding hydrogen (H₂) to NG. This is one of the methods applied to use natural gas in CI engines. In this experimental study, two different volumetric rates of NG and NG/H₂ mixtures were added to the combustion air in a CI engine, and engine performance and emissions were examined under different engine loads. The experiments were performed at two different engine speeds, four different engine loads and no-load condition. An engine cylinder pressure of 59.16 bar, which is the closest value to the 59.39 bar obtained in the use of diesel fuel, was obtained at 1500 rpm for “Diesel + NG(500 g/h)” and 59.9 bar (highest values) was obtained for “Diesel + (500 g/h) [80%NG+20%H₂]" at 1750 rpm. For “Diesel + NG(250 g/h)” (Mix1) and “Diesel + NG(500 g/h)” (Mix2), as the engine speed increases, at the point where the maximum in-cylinder pressure is obtained occurs further to the right from top dead center (TDC). With the addition of 500 g/h NG, an increase of 4.5% was achieved in the cylinder pressure at full load, while an increase of 6.5% was achieved in the case of using “Diesel + (500 g/h) [80%NG+20%H₂]". Although the effect of the NG and NG/H₂ mixtures on in-cylinder pressure was small, the fuel consumption and thermal efficiency improved. Substantial improvements in hydrocarbon (HC) emissions were observed with the use of “Diesel + (250 g/h)[80%NG+20%H₂]”. Carbon dioxide (CO₂) emissions decreased with speed increase, but no significant differences in terms of CO₂ emissions were observed between the mixtures. There was a maximum difference of 15% between the diesel and the mixtures in CO₂ emissions. Although there was a decrease in nitrogen oxide (NO_x) levels with the increase in engine speed, the lowest NO_x emissions of 447.6 ppmvol was observed in “Diesel + NG(250 g/h)” (Mix1) at 1750 rpm at maximum load.     

A numerical study on a hydrogen assisted diesel engine

This work aims to numerically study the performance, combustion and emission characteristics of a hydrogen assisted diesel engine under various operating conditions. Simulations were performed using multi-dimensional software KIVA4 coupled with CHEMKIN. The Kelvin–Helmholtz and Rayleigh–Taylor hybrid break up model was implemented to accurately model the spray development. A detailed reaction mechanism was constructed to take into account the chemical kinetics of diesel and hydrogen, and it was validated against the experimental results with 0% of hydrogen induction. Simulation results showed that at low engine speeds, the indicated thermal efficiency, in-cylinder pressure and apparent heat release rate increased significantly with the induction of hydrogen. On the other hand, at high engine speed and high load conditions, no tangible changes on the engine performance, combustion characteristics were observed. In terms of emissions, CO and soot emissions were shown to be reduced under most of the engine operating conditions. Whereas for NO_x emissions, a slight increase was observed at low engine speed of 1600 rpm.     

Effect of hydrogen and LPG addition on the efficiency and emissions of a dual fuel diesel engine

This paper presents some experimental investigations on dual fuel operation of a 4 cylinder (turbocharged and intercooled) 62.5 kW gen-set diesel engine with hydrogen, liquefied petroleum gas (LPG) and mixture of LPG and hydrogen as secondary fuels. Results on brake thermal efficiency and emissions, namely, un-burnt hydrocarbon (HC), carbon monoxide (CO), NO_x and smoke are presented here. The paper also includes vital information regarding performances of the engine at a wide range of load conditions with different gaseous fuel substitutions. When only hydrogen is used as secondary fuel, maximum enhancement in the brake thermal efficiency is 17% which is obtained with 30% of secondary fuel. When only LPG is used as secondary fuel, maximum enhancement in the brake thermal efficiency (of 6%) is obtained with 40% of secondary fuel. Compared to the pure diesel operation, proportion of un-burnt HC and CO increases, while, emission of NO_x and smoke reduces in both cases. On the other hand, when 40% of mixture of LPG and hydrogen is used (in the ratio 70:30) as secondary fuel, brake thermal efficiency enhances by 27% and HC emission reduces by 68%. Further, shortcoming of low efficiency at lower load condition in a dual fuel operation is removed when a mixture of hydrogen and LPG is used as the secondary fuel at higher than 10% load condition.     

Gas emissions and particulate matter of non-road diesel engine fueled with F-T diesel with EGR

The gas emissions and particulate matter of non-road diesel engine fueled with Fischer–Tropsch diesel fuel were investigated. The test was carried out on a four-stroke, water-cooled, single-cylinder engine under different the exhaust gas recirculation (EGR) rates such as 0%, 15%, and 30% at 2,700 rpm, 25%, 50%, and 75% load. The test results showed that when the EGR rate is less than 15%, nitrogen oxides (NO_x) are reduced significantly, while hydrocarbon (HC) and carbon monoxide (CO) are increased less than 5%. However, when the EGR rate was 30%, HC and CO were maximally increased to 13.2% and 13.3%, respectively. Additionally, the Field Emission Scanning Electronic Microscope test and Energy Dispersive Spectrometer test were conducted. With increase of EGR rates, the micromorphology of particles was mainly showed as chain-like status and the growth of number concentration of particle was mainly contributed by the nuclear particle when the engine was at 25% load. In contrast, the micromorphology of particles was principally showed as clustered-like status, and the aggregated particles were dominating growth at 50% and 75% load. Moreover, as EGR rates increased, the degree of agglomeration and carbon content were gradually decreased at 25% load. The test also showed the opposite tendency at 50% and 75% load.     

A review on various after treatment techniques to reduce NOx emissions in a CI engine

NOx emissions have always been a main concern in the development of diesel engines. This paper summarizes the studies about NOx emission reduction in diesel engines. The need for meeting the stringent requirements with regard to NOx emissions in a diesel engine has led to the development of a range of after treatment techniques. After treatment methods are required to reduce NOx emissions that cannot be controlled by fuel composition and combustion phenomena. Current after treatment techniques that are being employed are Selective Catalytic Reduction (SCR), Lean NOx Trap (LNT) and SCR Filter (SCRF). The benefits and constraints of different types of SCR are discussed. Urea SCR is a prominent well proven technology. Urea SCR produces 96–99% conversion efficiency with the help of a reductant NH₃. The operating parameters such as nature of catalyst, temperature range of catalyst, flow of DEF (Diesel Exhaust fluid) to injector and mixing of NH₃ and NOx are discussed. Hybrid SCR such as Cu-SCR + Fe-SCR, SCR + LNT moderates fuel consumption and augments the catalytic activity at low temperature. SCRF has low cell density (200–300 csi vs 400–600 csi for SCR), and also has lower deNOx efficiency for a number of reasons. Pre-stored NH₃ and Preheating helps in low temperature reaction of SCRF. Technical problems in aqueous urea systems have led to the evolution of solid SCR system (SSCR). This review incorporates the study of solid ammonium salts decomposition, temperature range of the salts and infrastructure required for SSCR.     

Experimental investigation of the effects of simultaneous hydrogen and nitrogen addition on the emissions and combustion of a diesel engine

Overcoming diesel engine emissions trade-off effects, especially NO_x and Bosch smoke number (BSN), requires investigation of novel systems which can potentially serve the automobile industry towards further emissions reduction. Enrichment of the intake charge with H₂ + N₂ containing gas mixture, obtained from diesel fuel reforming system, can lead to new generation low polluting diesel engines.     

Effect of H2 addition on combustion and exhaust emissions in a heavy-duty diesel engine with EGR

The effect of the addition of hydrogen (H₂) on the combustion process and nitric oxide (NO) formation in a H₂-diesel dual fuel engine was numerically investigated. The model developed using AVL FIRE as a platform was validated against the cylinder pressure and heat release rate measured with the addition of up to 6% (vol.) H₂ into the intake mixture of a heavy-duty diesel engine with exhaust gas recirculation (EGR). The validated model was applied to further explore the effect of the addition of 6%–18% (vol.) H₂ on the combustion process and formation of NO in H₂-diesel dual fuel engines. When the engine was at N = 1200 rpm and 70% load, the simulation results showed that the addition of H₂ prolonged ignition delay, enhanced premixed combustion, and promoted diffusion combustion of the diesel fuel. The maximum peak cylinder pressure was observed with addition of 12% (vol.) H₂. In comparison, the maximum peak heat release rate was observed with the addition of 16% (vol.) H₂. The addition of H₂ was a crucial factor dominating the increased NO emissions. Meanwhile, the addition of H₂ reduced soot emissions substantially, which may be due to the reduced diesel fuel burned each cycle. Furthermore, proper combination of adding H₂ with EGR can improve combustion performance and reduce NO emissions.     

Experimental investigation of the effects of separate hydrogen and nitrogen addition on the emissions and combustion of a diesel engine

An experimental investigation of the effects of separate hydrogen and nitrogen addition on the emissions and combustion of a diesel engine was performed and the results are presented in the current paper.     

Mixing and flame structures inferred from OH-PLIF for conventional and low-temperature diesel engine combustion

The structure of first- and second-stage combustion is investigated in a heavy-duty, single-cylinder optical engine using chemiluminescence imaging, Mie-scatter imaging of liquid-fuel, and OH planar laser-induced fluorescence (OH-PLIF) along with calculations of fluorescence quenching. Three different diesel combustion modes are studied: conventional non-diluted high-temperature combustion (HTC) with either (1) short or (2) long ignition delay, and (3) highly diluted low-temperature combustion (LTC) with early fuel injection. For the short ignition delay HTC condition, the OH fluorescence images show that second-stage combustion occurs mainly on the fuel jet periphery in a thickness of about 1 mm. For the long ignition delay HTC condition, the second-stage combustion zone on the jet periphery is thicker (5-6 mm). For the early-injection LTC condition, the second-stage combustion is even thicker (20-25 mm) and occurs only in the down-stream regions of the jet. The relationship between OH concentration and OH-PLIF intensity over a range of equivalence ratios is estimated from quenching calculations using collider species concentrations predicted by chemical kinetics simulations of combustion. The calculations show that both OH concentration and OH-PLIF intensity peak near stoichiometric mixtures and fall by an order of magnitude or more for equivalence ratios less than 0.2-0.4 and greater than 1.4-1.6. Using the OH fluorescence quenching predictions together with OH-PLIF images, quantitative boundaries for mixing are established for the three engine combustion modes.     

Hydrogen energy share enhancement in a heavy duty diesel engine under RCCI combustion fueled with natural gas and diesel oil

The aim of this study is to enhance hydrogen energy share in a RCCI engine. The engine under consideration is fueled with diesel oil and natural gas enriched with hydrogen or syngas and is set to operate at 9.4 bar gross indicated mean effective pressure (Mid- Load). The syngas used in this study consists of hydrogen and carbon monoxide which are mixed together on a volumetric ratio of 80:20. A fixed amount of diesel oil is injected per cycle into the combustion chamber of the RCCI engine. Based on two different strategies, hydrogen or syngas mixed with exhaust gas recirculation are admitted gradually along with natural gas while ensuring that always the low temperature combustion concept is fulfilled. The RCCI engine operation is simulated through commercial software coupled with chemical kinetics solver. The simulation results show that without any engine diesel knock occurrence, by adding hydrogen to natural gas, the share of hydrogen energy could be increased up to 40.43% while the engine power output is reduced only by about 1%. Also, syngas addition to natural gas causes that the share of hydrogen energy could be increased up to 27.05% while improves the engine power more than 4%. At the same time, by considering two mentioned strategies, the overall hydrocarbon fuel consumption per cycle can be reduced by up to 46.60% and 33.86%, respectively. Moreover, having the gross indicated efficiency of well over 50% and significant reduction in the engine emissions compared to RCCI combustion fueled solely with natural gas and diesel oil are achievable.     

Near-zero emissions with high thermal efficiency realized by optimizing jet plume location relative to combustion chamber wall,jet geometry and injection timing in a direct-injection hydrogen engine

Thermal efficiency was substantially improved and NOx emissions were reduced to a level at a single-digit ppm with PCC combustion by optimizing such characteristics as the direction, number and diameter of the injected jet and controlling the injection timing and also by combining with combustion of lean mixture. Output power declined by lean mixture was recovered by supercharging in keeping NOx emissions remained at the same level, while thermal efficiency was improved furthermore by slightly re-optimizing jet conditions. As a result, hydrogen engine which does not emit any CO2 and particulate matter in principle is worth to be called near-zero emission engines in both name and reality.     

Hydrogen combustion in a compression ignition diesel engine

The investigation presented in this paper concerns both pure hydrogen combustion under HCCI (homogeneous charge compression ignition) conditions and hydrogen–diesel co-combustion in a compression ignition (CI) engine.     

Efficiency and emissions of a spark ignition engine fueled with synthetic gases obtained from catalytic decomposition of biogas

This paper presents the results of the tests developed in a naturally aspirated spark ignition engine, intended for installation in vehicles, fueled with synthetic gases obtained from catalytic decomposition of biogas. The experimental tests were carried out at three equivalence ratios and different speeds and loads. Two synthetic blends were used and the results were compared with those of gasoline and methane. Efficiency and emissions were calculated for the different fuels under the same operation conditions and it was found that at lean equivalence ratios, brake thermal efficiency with synthetic gases approached to the traditional fuels and even improved it at Φ = 0.7. BSCO₂ emissions increased due to the CO₂ content of the gaseous blends. While CO increased at stoichiometric conditions, it decreased at lean conditions because the H₂ contained in synthetic gases improved combustion at these conditions. BSHC measured were very low with synthetic gases because of the low content of methane in blends. The change in the fraction of H₂ and CO₂ of the synthetic blends led to quite different results in BSNOx. Syngas 1 BSNOx emissions were the lowest of all fuels, while syngas 2 BSNOx were the highest because of its high H₂ fraction.     

Hydrogen impacts on performance and CO2 emissions from a diesel power generator

This work investigates the performance and carbon dioxide (CO₂) emissions from a stationary diesel engine fueled with diesel oil (B5) and hydrogen (H₂). The performance parameters investigated were specific fuel consumption, effective engine efficiency and volumetric efficiency. The engine was operated varying the nominal load from 0 kW to 40 kW, with diesel oil being directly injected in the combustion chamber. Hydrogen was injected in the intake manifold, substituting diesel oil in concentrations of 5%, 10%, 15% and 20% on energy basis, keeping the original settings of diesel oil injection. The results show that partial substitution of diesel oil by hydrogen at the test conditions does not affect significantly specific fuel consumption and effective engine efficiency, and decreases the volumetric efficiency by up to 6%. On the other hand the use of hydrogen reduced CO₂ emissions by up to 12%, indicating that it can be applied to engines to reduce global warming effects.     

CFD modeling and experimental study of combustion and nitric oxide emissions in hydrogen-fueled spark-ignition engine operating in a very wide range of EGR rates

In the current work, the variation of EGR rates is investigated in a hydrogen-fueled, spark-ignition engine. This technique is followed in order to control the engine load and decrease the exhaust nitrogen oxides emissions. The external EGR is varied in the very wide range of 12% up to 47% (by mass), where in each test case the in-cylinder mixture is stoichiometric, diluted with the appropriate EGR rate. The operation of this engine is explored using measured data with the aid of a validated CFD code. Moreover, a new residual gas term existing in the expression of the hydrogen laminar flame speed, which has been derived from a one-dimensional chemical kinetics code, is tested in a real application for appraising its capabilities. The investigation conducted provides insight on the performance and indicated efficiency of the engine, the combustion processes, and the emissions of nitrogen oxides. More precisely, an experimental study has been deployed with the aim to identify the characteristics of such a technique, using very high EGR rates, focusing on the combustion phenomena. At the same time, the CFD results are compared with the corresponding measured ones, in order to evaluate the CFD code under such non-conventional operating conditions and to test a recent expression for the residual gas term included in the hydrogen laminar flame speed expression. It is revealed that the combustion takes place in few degrees of crank angle, especially at high engine loads (low EGR rates), whereas the exhaust nitrogen oxides emissions are significantly decreased in comparison to the use of lean mixtures for controlling the engine load. Additionally, the recent expression of the residual gas term, which has been tested and incorporated in the CFD code, seems to be adequate for the calculation of combustion phenomena in highly diluted, with EGR, hydrogen-fueled spark-ignition engines, as for every EGR rate tested (even for the higher ones) the computational results are compared in good terms with the measured data.     

Study on the NOx emissions mechanism of an HICE under high load

A hydrogen fueled internal combustion engine (HICE) CFD simulation model consisting of detailed chemical reaction mechanisms was built using CONVERGE to study the NOx formation mechanisms. The Simulation Results are consistent with the experiments we had reported. The Simulation results show that the temperature inside the flame front and the OH concentration in the flame front increased with the fuel-air equivalence ratio. NO, as the major component of NOx, was generated abundantly during the rapid combustion period with the temperature rising and decreased after the rapid combustion period to a stable amount when the temperature dropped below 2200 K in cylinder. NO was generated mainly through three route named as thermal NO, NNH and N₂O. The Thermal NO path contributed a large proportion of the total NO emissions and the contribution increased with the fuel-air equivalence. NNH and N₂O routecontributed 24.2% of the total NO emissions when the fuel-air equivalence was 0.6, but contributed ?23.9% when the fuel-air equivalence was 1.0.