Simulation of combustion in spark-ignition engine fuelled with natural gas-hydrogen blends combined with EGR

Abstract

A numerical simulation of the influence of different hydrogen fractions, excess air ratios and EGR mass fractions in a spark-ignition engine was conducted. Good agreement between the calculated and measured in-cylinder pressure traces as well as pollutant formation trends was obtained. The simulation results show that NO concentration has an exponential relationship with temperature and increases sharply as hydrogen is added. EGR introduction strongly influences the gas temperature and NO concentration in the cylinder. The difference in temperature will lead to even greater difference in NO concentration. Thus, EGR can effectively decrease NO concentration. NO concentration reaches its peak value at the excess air ratio of 1.1 regardless of EGR mass fraction. The study shows that natural gas-hydrogen blend combined with EGR can realize a stable combustion and low NO emission in a spark-ignition engine.

Key words： natural gas; hydrogen; NO; exhaust gas recirculation; numerical simulation

Acknowledgements

The study was sponsored by the National Natural Science Foundation of China (Grant No. 50636040) and the National Basic Research Program of China (No. 2007CB210006).

Notations

CNG	compressed natural gas
EGR	exhaust gas recirculation
TDC	top dead center
BDC	bottom dead center
ATDC	after top dead center
BTDC	before top dead center
WOT	wide open throttle
λ	excess air ratio
n	engine speed
φ(H2)	hydrogen mass fraction
φ	crank angle
φig	ignition time by crank angle scale
T	mean cylinder temperature
p	mean cylinder pressure

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