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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]

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: The paper presents results and discussion on syngas combustion in a spark ignited internal combustion engine driving a power generator (16kW/1500rpm). The syngas applied as the engine fuel is produced by gasifying municipal sewage sludge. Unlike fermentation biogas, the syngas obtained from sewage sludge gasification is found a fuel, which generates several difficulties (non-stable combustion, misfiring events) while burning in the SI engine. The analysis of cycle-by-cycle engine run shows that the engine working on syngas features will run unsteadily due to the occurrence of misfiring events caused by the relatively low calorific value of the syngas. Thus, combustion of such a syngas in the SI IC engine can generate malfunctions. Therefore, the syngas was enriched with methane at various ratios starting from 0% up to 60% by volume. The impact of methane addition on the engine performance and exhaust emission was also presented in the paper. As investigated, 40% methane enrichment in the syngas was found sufficient amounts to obtain satisfactory engine run. Thus, in practice, the syngas from sewage sludge gasification is a troublesome fuel, but can satisfactorily be applied to the SI engine when enriched with natural gas or biogas. [Copyright &y& Elsevier]

Investigation of a new type of fuel for the internal combustion engine, which can be successfully used in both the power generation and the automotive industries, is presented in this article. The proposed fuel is a blend of 75% n-butanol and 25% glycerol. The engine tests conducted with this glycerol–butanol blend were focused on the performance, combustion thermodynamics, and exhaust emissions of a spark-ignition engine. A comparative analysis was performed to find potential similarities and differences in the engine fueled with gasoline 95 and the proposed glycerol–butanol blend. As measured, CO exhaust emissions increased, NOx emissions decreased, and UHC emissions were unchanged for the glycerol–butanol blend when compared to the test with sole gasoline. As regards the engine performance and combustion progress, no significant differences were observed. Exhaust temperature remarkably decreased by 3.4%, which contributed to an increase in the indicated mean effective pressure by approximately 4% compared to gasoline 95. To summarize, the proposed glycerol–butanol blend can be directly used as a replacement for gasoline in internal combustion spark-ignition engines. [ABSTRACT FROM AUTHOR]