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.     

Hydrogen and propane implications for reactivity controlled compression ignition combustion engine running on landfill gas and diesel fuel

A detailed investigation of employing landfill gas together with additives such as hydrogen or propane or both as a primary low reactivity fuel in a reactivity controlled compression ignition combustion of a diesel engine is conducted. A 3401E caterpillar single-cylinder diesel engine with a bathtub piston bowl profile is utilized to execute the study. The engine is operated at various intake pressures of 1.6, 1.9, and 2.2 bar, and runs at a fixed engine speed of 1300 rpm. For verification purposes, the conduct of the present engine running on pure methane as a low reactivity fuel is compared to that of the same engine available in the literature. Next, a numerical simulation is made to assess the performance of the present engine running on landfill gas plus the additives. Based on the obtained results, injecting either hydrogen or propane or a combination of both up to a total amount of 10% by volume to the premixed of landfill gas and air, and advancing diesel fuel injection timing of about 20–30 deg. crank angle, render the landfill gas utilization quite competitive with using methane alone. Applying an enriched landfill gas in a reactivity controlled compression ignition diesel engine, as a power generator, drastically reduces the greenhouse gas emission to the atmosphere. Also, the CO and UHC mole fraction in the exhaust gas can be eliminated by either advancing the start of diesel injection or using hydrogen or propane or both as additives. In addition, utilizing hydrogen or propane or a combination of both with the primary fuel improves the peak pressure to about 16% in comparison with that of landfill gas alone.     

A detail study of a RCCI engine performance fueled with diesel fuel and natural gas blended with syngas with different compositions

The catalytic reforming is an applicable method to generate hydrogen as an alliterative fuel directly that is of prime interest to replace hydrocarbon fuels. Although, the use of this type of catalyst has the potential to solve the problem of safe storage of hydrogen in ICEs, but, this method suffers from the simultaneous production of carbon monoxide with hydrogen known as syngas. Depending on the engine operating conditions, different syngas composition in terms of H2/CO volumetric ratio can be produced through the mentioned catalyst. An engine performance which uses onboard hydrogen produced is completely affected by syngas composition. Therefore, the aim of the current simulation study is to evaluate the performance of a heavy-duty diesel engine under RCCI combustion fueled with diesel fuel/natural gas blended with syngas with different compositions. For this purpose, at 9.4 bar gross IMEP, natural gas is gradually replaced by five different compositions of syngas that is H2/CO volumetric ratios of 33.33/66.67, 50/50, 66.67/33.33, 80/20, and 100/0. The simulation results show that not only the engine output power can be improved up to 27.7% by simply increasing of the CO/H2 volumetric ratio in syngas composition to 66.67/33.33, but also the GIE is reduced by less than 9%. In contrast, the risk of the diesel knock occurrence may increase only in higher CO/H2 ratios. Although, the NOx level can be achieved closer to the EURO VI level, but, same level for UHC and CO and also the level of EPA 2007 for formaldehyde are not achievable for syngas with the higher CO/H2 volumetric ratio.     

Numerical study on knock characteristics and mechanism of a heavy duty natural gas/diesel RCCI engine

In this paper, the knock phenomenon of reactivity controlled compression ignition (RCCI) engine fueled with natural gas/diesel was numerically studied. The knock mechanism of the RCCI engine is explained and the strategy of suppressing knock is put forward. The knock characteristics were studied by setting monitoring points in different spaces positions of the cylinder. The results show that the pressure oscillation amplitude at the center and edge of the cylinder is large under the high load condition of RCCI engine. In addition, the knock mechanism was studied by using pressure difference method, maximum amplitude of pressure oscillation, important components, temperature isosurface, pressure fluctuation and heat release rate. The results show that the knock of RCCI engine is mainly caused by the end-gas auto-ignition. The pressure difference results show that the characteristic frequency is consistent with the natural resonance mode (0,1) of the cylindrical combustion chamber. On this basis, the effects of pilot oil injection timing and compression ratio on engine knock are further studied. It is confirmed that diesel knock and end-gas knock may exist simultaneously in the same cycle when RCCI engine knock occurs. And diesel knock occurs before top dead center, and end-gas knock occurs after top dead center. Proper adjustment of pilot oil injection timing and reduction of compression ratio can effectively suppress engine knock.     

Effect of hydrogen addition to intake air on combustion noise from a diesel engine

This study investigates the characteristics of combustion noise from a diesel engine with hydrogen added to intake air. The engine noise with hydrogen addition of 10 vol% to the intake air was lower than that with diesel fuel alone at late diesel-fuel injection timings. A transient combustion-noise-generation model was introduced to discuss noise characteristics based on energy conversion from combustion impact to noise via structure vibration. The results show that the maximum combustion impact energy had a predominant effect on the maximum engine noise power for each cycle. Therefore, the combustion noise largely contributed to the total engine noise in an early stage of the expansion stroke. The dependences of engine noise on the diesel-fuel injection timing for different hydrogen fractions are discussed considering the characteristics of maximum combustion impact energy for each frequency.     

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.     

Effect of natural gas enrichment with hydrogen on combustion characteristics of a dual fuel diesel engine

Environmental benefits are one of the main motivations encouraging the use of natural gas as fuel for internal combustion engines. In addition to the better impact on pollution, natural gas is available in many areas. In this context, the present work investigates the effect of hydrogen addition to natural gas in dual fuel mode, on combustion characteristics improvement, in relation with engine performance. Various hydrogen fractions (10, 20 and 30 by v%) are examined. Results showed that natural gas enrichment with hydrogen leads in general to an improved gaseous fuel combustion, which corresponds to an enhanced heat release rate during gaseous fuel premixed phase, resulting in an increase in the in-cylinder peak pressure, especially at high engine load (4.1 bar at 70% load). The highest cumulative and rate of heat release correspond to 10% Hydrogen addition. The combustion duration of gaseous fuel combustion phase is reduced for all hydrogen blends. Moreover, this technique resulted in better combustion stability. For all hydrogen test blends, COV_IMEP does not exceed 10%. However, no major effect on combustion noise was noticed and the ignition delay was not affected significantly. Regarding performance, an important improvement in energy conversion was obtained with almost all hydrogen blends as a result of improved gaseous fuel combustion. A maximum thermal efficiency of 32.5%, almost similar to the one under diesel operation, and a minimum fuel consumption of 236 g/kWh, are achieved with 10% hydrogen enrichment at 70% engine load.     

Performance and combustion characteristic of CI engine fueled with hydrogen enriched diesel

The combustion of hydrogen–diesel blend fuel was investigated under simulated direct injection (DI) diesel engine conditions. The investigation presented in this paper concerns numerical analysis of neat diesel combustion mode and hydrogen enriched diesel combustion in a compression ignition (CI) engine. The parameters varied in this simulation included: H₂/diesel blend fuel ratio, engine speed, and air/fuel ratio. The study on the simultaneous combustion of hydrogen and diesel fuel was conducted with various hydrogen doses in the range from 0.05% to 50% (by volume) for different engine speed from 1000 – 4000 rpm and air/fuel ratios (A/F) varies from 10 – 80. The results show that, applying hydrogen as an extra fuel, which can be added to diesel fuel in the (CI) engine results in improved engine performance and reduce emissions compared to the case of neat diesel operation because this measure approaches the combustion process to constant volume. Moreover, small amounts of hydrogen when added to a diesel engine shorten the diesel ignition lag and, in this way, decrease the rate of pressure rise which provides better conditions for soft run of the engine. Comparative results are given for various hydrogen/diesel ratio, engine speeds and loads for conventional Diesel and dual fuel operation, revealing the effect of dual fuel combustion on engine performance and exhaust emissions.     

Effect of hydrogen addition on the combustion and emission of a diesel free-piston engine

The free-piston engine (FPE) is a new crankless engine, which operates with variable compression ratio, flexible fuel applicability and low pollution potential. A numerical model which couples with dynamic, combustion and gas exchange was established and verified by experiment to simulate the effects of different hydrogen addition on the combustion and emission of a diesel FPE. Results indicate that a small amount of hydrogen addition has a little effect on the combustion process of the FPE. However, when the ratio of hydrogen addition (R_H2) is more than 0.1, the R_H2 gives a positive effect on the peak in-cylinder gas pressure, temperature, and nitric oxide emission of the FPE, while soot emission decreases with the increase of hydrogen addition. Moreover, the larger R_H2 induces a longer ignition delay, shorter rapid combustion period, weaker post-combustion effect, greater heat release rate, and earlier peak heat release rate for the FPE. Nevertheless, the released heat in rapid combustion period is significantly enhanced by the increase of R_H2.     

Effect of reformed biogas as a low reactivity fuel on performance and emissions of a RCCI engine with reformed biogas/diesel dual-fuel combustion

Biogas can be used as a less expensive continuance renewable fuel in internal combustion engines. However, variety in raw materials and process of biogas production results in different components and percentages of various elements, including methane. These differences make it difficult to control the combustion, effectively, in internal combustion engines. In this research, under cleaning and reforming process, biogas components were fixed. Then the effect of reformed biogas (R.BG) was investigated, numerically, on the combustion behavior, performance and emissions characteristics of a RCCI engine. A 3D-computational modeling has been performed to validate a single-cylinder compression ignition engine in conventional diesel and dual-fuel operations at 9 bar IMEP, 1300 rpm. Then, the combustion model of the RCCI engine was simulated by replacing diesel fuel with 20%, 40% and 60% of R.BG as a low reactivity fuel while remaining constant input total fuel energy per cycle. The results demonstrated that when the R.BG substitution ratio increases with a constant equivalence ratio of 0.43, the mean combustion temperature decreases to 1354 K, 1312 K, 1292 K which are about 3.5%, 6.6%, 7.9% lower than the conventional diesel combustion, respectively. The maximum in-cylinder pressure increases up to 22.63%. Instead, it results in 2.3%, 7.9%, and 14.5% engine power output losses, respectively. Also, the NOx emission, against CO, is decreased by 50%. Soot and UHC emissions were found to be slightly decreased while was used R.BG more than 40%.     

Experimental and numerical study of hydrogen addition in a natural gas heavy duty engine for a bus vehicle

Hydrogen added to natural gas improves the process of combustion with the possibility to develop engines with higher performance and lower environmental impact. In this paper experimental and numerical analyses on a multi cylinder stoichiometric heavy duty engine, fuelled with natural gas–hydrogen blends, are reported. Some constrains on hydrogen content and maximum load achievable have limited the scope of investigation. A specific modelling of the reference engine was developed to extend the study at full load condition and at higher hydrogen content. The results showed a higher combustion speed when hydrogen content in the fuel is increased. However, the positive effect of shorter combustion duration on thermal efficiency is mitigated by higher wall heat loss, due to higher combustion temperatures. Therefore lower CO₂ emissions are due only to the substitution of natural gas with hydrogen, making crucial the way of hydrogen producing to have a benefit on well-to-wheel CO₂ emissions.     

Combustion,performance and emissions of ULSD,PME and B50 fueled multi-cylinder diesel engine with naturally aspirated hydrogen

An experimental study was conducted on a diesel engine fueled with ultra-low sulfur diesel (ULSD), palm methyl ester (PME), a blended fuel containing 50% by volume each of the ULSD and PME, and naturally aspirated hydrogen, at an engine speed of 1800 rev min⁻¹ under five loads. Hydrogen was added to provide 10% and 20% of the total fuel energy. The following results are obtained with hydrogen addition. There is little change in peak in-cylinder pressure and peak heat release rate. The influence on fuel consumption and brake thermal efficiency is engine load and fuel dependent; being negative for the three liquid fuels at low engine loads but positive for ULSD and B50 and negligible for PME at medium-to-high loads. CO and CO₂ emissions decrease. HC decreases at medium-to-high loads, but increases at low loads. NO_x emission increases for PME only but NO₂ increases for the three liquid fuels. Smoke opacity, particle mass and number concentrations are all reduced for the three liquid fuels.     

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.     

1D energy,exergy, and performance assessment of turbocharged diesel/hydrogen RCCI engine at different levels of diesel,hydrogen, compressor pressure ratio,and combustion duration

There is a growing concern about the feasibility of a new generation of internal combustion engines in a low-temperature and efficient way that can meet the emission regulations while maintaining the desirable power performance. This requires the controllability and flexibility over the ignition and reactivity within the cylinder by handling two fuels with different chemical reaction intensity. In this research, the reactivity controlled compression ignition (RCCI) turbocharger-assisted engine is proposed that operates with diesel-hydrogen fuels. After calibration and model validation, the effect of pressure ratio of compressor in turbocharger, hydrogen energy share, diesel mass per cycle, and combustion duration on temperature rise, entropy, pressure, heat release, and engine performance is evaluated. The design variables effects on the exergy share of work, heat, exhaust loss, irreversibility, and exergetic performance coefficient (EPC) are assessed and analyzed. Increasing the compressor pressure ratio can significantly increase the engine power and reduce fuel consumption. It is proved that turbocharging can reduce the entropy generation and thereby reduce irreversibility. The lower diesel injection is favored in terms of the work exergy and the EPC.     

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.     

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 excess hydrogen on hydrogen fueled internal combustion engine under full load

Detailed hydrogen-air chemical reaction mechanisms were coupled with three dimension grids of an experimental hydrogen fueled internal combustion engine (HICE) to establish a combustion model based on CONVERGE software. The influence of excess hydrogen coefficient on the combustion and emission characteristics of HICE under full load was studied based on the CFD model. Simulation results showed that excess hydrogen leaded to higher concentration of OH species in flame front, and quicker hydrogen-oxygen reaction and flame propagation speed, which in turn leaded to higher pressure and temperature in cylinder. The rise of pressure and temperature in turn contributed to the increase of indicate power but un-burned hydrogen leaded to decrease of efficiency. NOx, especially NO emissions decreased significantly with excess hydrogen under full load not only because increased of H concentration, and decreased of O and OH concentration, which leaded to reverse reaction of NO formation through thermal NO routes. Low excess hydrogen coefficient can achieve a good trade-off between power and emissions under full load.     

Effect of hydrogen addition to intake gas on combustion and exhaust emission characteristics of a diesel engine

The present study experimentally investigated the performance and emission characteristics of the diesel engine with hydrogen added to the intake air at late diesel-fuel injection timings. The diesel-fuel injection timing and the hydrogen fraction in the intake mixture were varied while the available heat produced by diesel-fuel and hydrogen per second of diesel fuel and hydrogen was kept constant at a certain value. NO showed minimum at specific hydrogen fraction. The maximum rate of incylinder pressure rise also showed minimum at 10 vol. % hydrogen fraction. However, it is desirable to set the maximum rate of incylinder pressure rise less than 0.5 MPa/deg. to realize low level of combustion noise and NO emission. We attempt to reduce further NO and smoke emissions by EGR. As the result, in the case of the diesel-fuel injection timing of −2 °. ATDC with 3.9 vol. % hydrogen addition, the smoke emission value was 0%, NO emission was low, the cyclic variation was low, and the maximum rate of incylinder pressure rise was acceptable under a nearly stoichiometric condition without sacrificing indicated thermal efficiency.     

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.     

Hydrogen enrichment effects on the second law analysis of natural and landfill gas combustion in engine cylinders

The availability (exergy) balance during combustion of hydrogen-enriched natural and landfill gas, which are used as fuels in combustion engine cylinders, is studied computationally using a zero-dimensional model of the closed part of the cycle. The main focus is on the demonstration of a fundamental difference in the generation of irreversibility during combustion between hydrogen and hydrocarbons. This difference relates to the mechanisms of entropy generation during the oxidation reaction of the two fuels and yields the particularly attractive characteristic of a monotonic decrease in combustion irreversibility with increasing hydrogen content of the fuel, for mole fractions of hydrogen smaller than 10%. This reduction in combustion irreversibility is reflected in an increase in second law efficiency with increasing proportions of hydrogen. The exhaust gas availability at the end of the closed part of the cycle was found to have a local maximum for a hydrogen mole fraction of the order of 5%. These trends with respect to hydrogen also apply when the fuel is diluted with a significant amount of CO₂ (of the order of 40%, as for example in the case for landfill gas), although the absolute value of each of the terms of the availability balance is affected strongly by the dilution.