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

Abstract

CFD modeling and experimental study of combustion and nitric oxide emissions in hydrogenfueled spark-ignition engine operating in a very wide range of EGR rates To refer to or to cite this work, please use the citation to the published version:Kosmadakis, G.D., Rakopoulos, C.D., Demuynck, J., De Paepe, M. & Verhelst, S. (2012). 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. INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 37(14) ABSTRACTIn the current work, the variation of EGR rates is investigated in a hydrogen-fueled, sparkignition 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.

Spark-Ignition Engine Fueled with Methane-Hydrogen Blends

“…It has been validated in previous published works (Kosmadakis et al 2012;Kosmadakis and Rakopoulos 2014a, b;Rakopoulos et al 2010aRakopoulos et al , 2011, where it has been revealed that it can adequately simulate the power cycle of hydrogen-fueled spark-ignition engines. In the next subsections the extended combustion model is briefly presented, as applied in the present study and its main differences with the addition of methane fuel are discussed.…”

“…In the next subsections the extended combustion model is briefly presented, as applied in the present study and its main differences with the addition of methane fuel are discussed. A detailed presentation can be found in previous publications (Kosmadakis et al 2012(Kosmadakis et al , 2013Kosmadakis and Rakopoulos 2014a, b;Rakopoulos et al 2010aRakopoulos et al , b, 2011.…”

“…The main difference here is that methane fuel and carbon chemistry are added in the transport equations. Only its basic features are given, since its detailed presentation is provided in previous publications (Kosmadakis et al 2012;Rakopoulos et al 2010a). …”

“…Moreover, many internal combustion engines, usually converted from commercial compression-or spark-ignition engines, have been fueled with various alternative gaseous fuels, such as the most common methane (or natural gas) and liquefied petroleum gas to the most rarely syngas and biogas, for use in power generation and transportation, showing inherently clean nature of combustion with reduced emitted pollutants (Papagiannakis and Zannis 2013;Rakopoulos and Kyritsis 2006;Rakopoulos and Michos 2009). Finally, fuel blends show some interesting features, especially when hydrogen is added to a conventional fuel for combustion enhancement, due to its very high combustion speed (Kosmadakis et al 2012).…”

“…This model has been initially developed for the simulation of the power cycle of hydrogen-fueled SI engines, and validated over many different conditions, including variable ignition timing, compression ratio, large range of equivalence ratios, and EGR (Kosmadakis et al 2012;Kosmadakis and Rakopoulos 2014a, b;Rakopoulos et al 2010aRakopoulos et al , 2011. The extension of this combustion model and of the CFD code mainly concerns the introduction of the carbon chemistry.…”