Cycle-by-cycle Variations in a Direct Injection Hydrogen Enriched Compressed Natural Gas Engine Employing EGR at Relative Air-Fuel Ratios.

Abstract

Abstract. Since the pressure development in a combustion chamber is uniquely related to the combustion process, substantial variations in the combustion process on a cycle-by-cycle basis are occurring. To this end, an experimental study of cycle-by-cycle variation in a direct injection spark ignition engine fueled with natural gashydrogen blends combined with exhaust gas recirculation at relative air-fuel ratios was conducted. The impacts of relative air-fuel ratios (i.e. λ = 1.0, 1.2, 1.3 and 1.4 which represent stoichiometric, moderately lean, lean and very lean mixtures respectively), hydrogen fractions and EGR rates were studied. The results showed that increasing the relative air-fuel ratio increases the COVIMEP. The behavior is more pronounced at the larger relative air-fuel ratios. More so, for a specified EGR rate; increasing the hydrogen fractions decreases the maximum COVIMEP value just as increasing in EGR rates increases the maximum COVIMEP value. (i.e. When percentage EGR rates is increased from 0% to 17% and 20% respectively. The maximum COVIMEP value increases from 6.25% to 6.56% and 8.30% respectively). Since the introduction of hydrogen gas reduces the cycle-by-cycle combustion variation in engine cylinder; thus it can be concluded that addition of hydrogen into direct injection compressed natural gas engine employing EGR at various relative air-fuel ratios is a viable approach to obtain an improved combustion quality which correspond to lower coefficient of variation in imep, (COVIMEP ) in a direct injection compressed natural gas engine employing EGR at relative air-fuel ratios.Keywords-Coefficient of variation in indicated mean effective pressure (COVIMEP); Direct injection compressed natural gas (DI-CNG); Exhaust gas recirculation (EGR); Hydrogen fractions; Relative air-fuel ratios.

Effects of Hydrogen Addition Ratios on Cycle-by-Cycle Variations of a Duel-Fuel Spark Ignition Engine with Ethanol Intake Port Injection and Hydrogen Direct Injection under Various Excess Air Ratios

“…The cyclic variation is related to many factors, including change of the intake flow field and distribution of the fuel concentration. , These factors are difficult to achieve precise control on the internal combustion engine. Under the lean-burn condition and exhaust gas recirculation (EGR) introduction, it is easy to cause instability of SI and flame propagation, thus leading to large cyclic variation. , In terms of the evaluation parameters of the cyclic variation, the indicated mean effective pressure and the peak in-cylinder pressure of the engine become the parameters that evaluate the cyclic variation. Different evaluation parameters have different sensitivities to changes of different factors. − In the field of the internal combustion engine, hydrogen addition is a good method to reduce the cyclic variation of the engine.…”

“…Under the lean-burn condition and exhaust gas recirculation (EGR) introduction, it is easy to cause instability of SI and flame propagation, thus leading to large cyclic variation. 36,37 In terms of the evaluation parameters of the cyclic variation, the indicated mean effective pressure and the peak incylinder pressure of the engine become the parameters that evaluate the cyclic variation. Different evaluation parameters have different sensitivities to changes of different factors.…”