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Hydrogen as potential engine fuel can appear either as a single gas or as a component in processing gases e.g. syngas, hythane and coke gas. The research in this paper investigates impact of combustible mixture dilution on abnormal combustion called knock in the reciprocating internal combustion engine. Dilution can be realized by either exhaust gas recirculation (EGR) or making the combustible mixture lean. Novelty of this work is a new metrics defined as dilution ratio, which makes it possible to compare knock reduction caused by either EGR or leaning the air-gas mixture to the engine. Two gaseous fuels were investigated: hydrogen and coke gas with 65% hydrogen. Conclusion based on the proposed dilution ratio states that, for hydrogen as the fuel, applying EGR is more effective in knock reduction than making the mixture lean. It was found that EGR strategy in the hydrogen fueled engine can reduce knock intensity from initial 40 kPa–20 kPa, whereas by leaning the mixture to the same dilution ratio, the knock is reduced to approximately 28 kPa. With respect to coke gas, it is proved that both EGR and lean mixtures influence on knock reduction at the same strength. • Combustible mixture dilution impact on combustion knock intensity. • Dilution ratio as a metrics for both exhaust gas recirculation and lambda. • Engine knock reduced more effectively by applying exhaust gases recirculation. • The correlation between dilution ratio and knock intensity is almost linear. [ABSTRACT FROM AUTHOR]

The main objective of this study was to examine impact of hydrogen addition to the compression ignition engine fueled with either rapeseed methyl ester (RME) or 7% RME blended diesel fuel (RME7) on combustion phases and ignition delay as well as smoke and exhaust toxic emissions. Literature review shows in general, hydrogen in those cases is used in small amounts below lower flammability limits. Novelty of this work is in applying hydrogen at amounts up to 44% by energy as secondary fuel to the compression ignition engine. Results from experiments show that increase of hydrogen into the engine makes ignition delay shortened that also affects main combustion phase. In all tests the trends of exhaust HC and CO toxic emissions vs. hydrogen addition were negative. The trend of smokiness decreased steadily with increase of hydrogen. Amounts of hydrogen addition by energy share were limited to nearly 35% due to combustion knock occurring at nominal load. • Hydrogen as secondary fuel for the diesel engine. • Main combustion phase and ignition delay shorten with hydrogen addition. • Indicated thermal efficiency stays not changed remarkably. • Hydrogen addition decreases smokiness, unburnt hydrocarbons and carbon monoxide. • Knock occurred at hydrogen addition over 35% by energy. [ABSTRACT FROM AUTHOR]

Exhaust gases remaining inside the engine cylinder after the exhaust stroke premix with fresh air-fuel combustible mixture and affect combustion process in the engine cylinder. Due to significantly higher temperature of these exhaust residuals (ExR) compared to the external exhaust gases recirculation (EGR), their impact on the in-cylinder combustion process is also different from impact of EGR. To control amounts of ExR independent of engine working parameters, the variable valve timing was introduced. It is known that variable valve timing affects not only volumetric efficiency and performance of the internal combustion reciprocating engine but also influences the amount of exhaust residuals remaining in the engine cylinder. These exhaust residuals impact combustion rates, combustion stability, knock and also play crucial role on exhaust toxic emissions. In this manuscript, the effect of variable valve overlap was studied on A. exhaust toxic emission (NOx, CO and THC), and B. combustion phasing and engine performance on a spark ignited natural gas fueled engine. The investigation was carried out in a single cylinder research engine at constant load. The engine was equipped with high authority dual independent cam phasors for both intake and exhaust values, but for the purpose of this study, the exhaust valve timing was fixed and intake valve timing was changed to vary the amount of exhaust residuals remaining in the engine cylinder. The correlation between valve overlap and exhaust residuals were determined. It was observed that correlation in the positive overlap range between 55 and 85 deg was almost positive linear. Regarding toxic exhaust emission, increase in exhaust residuals from 9.6 to 12.3% (change by 28%) caused reduction in NOx by 67% and increase in both CO and THC by approximately 75%. Additionally, it did not significantly affect the engine’s specific fuel consumption. Summarizing, strong correlation between in-cylinder exhaust residuals and toxic emissions, and combustion phases exists in the methane fueled spark ignited engine equipped with VVT. [ABSTRACT FROM AUTHOR]

The paper presents results from investigation on a new type of fuel which can be implemented for the both automotive and power industry. The proposed fuel is of a completely renewable origin based on ethanol and glycerol at the ratio of 3:1 (75% and 25%), respectively. Hence, it does not contribute to unsustainable CO 2 emissions to the atmosphere. The analysis of combusting the ethanol-glycerol blend in the spark-ignited reciprocating engine was focused on engine performance, combustion thermodynamics, and toxicity content in the exhaust gases. The analysis was conducted as a comparative analysis for gasoline and ethanol, which were treated as reference fuels. The toxic emissions of CO, NOx, and unburnt hydrocarbons (UHC) did not differ remarkably from the gasoline emissions tests. The engine performance expressed by the indicated mean effective pressure deteriorated less than 3%. It was found that the ethanol-glycerol blend at the ratio of 3:1 (75/25%) can be directly applied as a substitute fuel for either gasoline or ethanol in internal combustion engines in the automotive and power industry. [Display omitted] • Investigation of ethanol-glycerol blend (3,1) for the internal combustion engine. • The engine performance (IMEP) deteriorated less than 3%. • Exhaust emissions of the blend are at similar level of gasoline 95 emissions tests. • Ethanol-glycerol blend can be applied as fuel for the spark-ignited engine. • Glycerol blended ethanol - considered an economic and energy-effective technology. [ABSTRACT FROM AUTHOR]

Abstract: Combustion knock is abnormal combustion taking place in an internal combustion spark ignited engine. It might be particularly observed in the engine at the end of combustion when the air–fuel mixture residue can be self-ignited due to exceeding auto-ignition temperature of this mixture. However, while hydrogen is combusted the knock can also occur as a result of non-auto-ignited combustion events. Investigation on knock, presented in the manuscript, was conducted in a hydrogen fueled spark ignited single cylinder engine with variable compression ratio. To express in numbers intensity of the combustion knock the in-cylinder pressure pulsations were used as a credible metrics. On the basis of analysis of these pulsations the hydrogen knock was distinguished as light and heavy one depending on its origin. The light knock is generated by combustion instabilities, which are a source for generating pressure waves inside the engine cylinder. The heavy knock results from hydrogen auto-ignition at the end of combustion. Its intensity is several times higher in comparison to the light knock. These observations were additionally confirmed by analysis of heat release rate. Finally, the light and the heavy knock were characterized by average amplitude of the pulsations from the entire test series of hundreds and several thousands kPa, respectively. [Copyright &y& Elsevier]

Abstract: The paper mainly focuses on applying the two-stage combustion system with a pre-chamber into the stationary internal combustion spark ignited engine. It especially concentrates on applying throttle less operation at partial load and reduction of the NO x emission. Considerations conducted in the paper are based on the in-cylinder combustion progress analysis. Additionally, analysis of tailpipe toxic emission, with particular focus on the NO x formation in the engine equipped with the pre-chamber, is also performed. The paper presents both results of 3-D combustion modeling in the SI engine and results conducted on a test SI engine. The 3-D modeling was performed in the KIVA-3V code. Next, results from modeling were compared with results obtained from tests. Finally, satisfactory good consistency between modeled and experimental courses of both pressure, temperature and NO x were obtained. Thus, the engine model with the proposed two-stage combustion system properly simulates engine working conditions on the test bed. Results from both analyses confirmed that the two-stage combustion system significantly shortens combustion duration of an ultra lean gasoline–air mixture and contributes to reduction in NO x . [Copyright &y& Elsevier]

Abstract: 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. The investigation on the simultaneous combustion of hydrogen and diesel fuel was conducted with various hydrogen doses in the range from 0% to 17% with respect to energy percentage. With hydrogen of 17% the hydrogen–diesel–air mixture was stoichiometric and provided favorable conditions for generating combustion knock. Small amounts of hydrogen (about 5%) when added to a diesel engine shorten the diesel ignition lag and, in this way, decrease the rate of pressure rise. It provides better conditions for soft run of the engine and can increase engine durability. The final conclusions concerning hydrogen impact on combustion knock intensity, mass fraction burned (MFB) and heat release rate of the engine are detailed. [Copyright &y& Elsevier]