A NUMERICAL STUDY OF NATURAL-GAS COMBUSTION IN A LEAN BURN ENGINE

Results from multidimensional numerical simulations and cycle simulati ons are presented in an effort to optimize the performance of a fuel-l ean-burn, homogeneous charge, natural gas spark-ignition internal comb ustion OC) engine. The multidimensional numerical simulations are perf ormed using modified versions of the KIVA-2 and KIVA-3 computer codes. The engine cycle simulations are performed using the WAVE code. The K IVA codes are enhanced with a turbulent combustion submodel which empl oys a two-step, natural gas/air chemical kinetics scheme with a temper ature-dependent activation energy, together with a modified eddy dissi pation model to treat the effects of turbulence on the burning rate. T he output from the multidimensional calculations is used, in a novel w ay, as input to the WAVE cycle simulation code to predict overall engi ne performance. The Caterpillar G3400 and G3500 fuel-lean-burn natural gas engines are the specific engines under study. The predictions for brake specific fuel consumption (BSFC) are within 1% of the measured values for all cases where engine data are available. The effects of s wirl, combustion chamber geometry, and spark location on burning rate and BSFC are investigated. Specifically, the results show that: (1) th e numerical predictions are in good qualitative and quantitative agree ment with engine data; (2) there is an optimum initial swirl ratio for the central bowl, central spark plug geometry; (3) an offset bowl res ults in a lower BSFC than a central bowl for the same initial swirl ra tio and spark plug location; and (4) an offset spark plug results in a lower BSFC than a central plug for the same initial swirl ratio. (C) 1998 Elsevier Science Ltd. All rights reserved.