(3-03) Feasibility of CNG DI Stratified Combustion Using a Spark-Ignited Rapid Compression Machine((AF-1)Alternative Fuels 1-Gas Engines)

Abstract

Characteristics of combustion and emissions of natural gas direct-injection (CNG DI) were studied by using a rapid compression machine. Results show that CNG DISC has the short overall combustion duration (Fig. 7(d)), high pressure rise due to combustion, and high rate of heat release (Fig. 12), which are considered to come from the charge stratification. The CNG DI can realize extremely lean combustion (Fig. 7(d)). Unburned methane showed almost the same level as that of homogeneous mixture combustion. CO increased steeply with the increase in equivalence ratio φ when φ was greater than 0.8 due to the excessive stratification, and NOx peak value shifted to the region of lower φ. Combustion inefficiency maintains less than 0.08 in the range of φ from 0.1 to 0.9(Fig. 1O(b)) and increases at very low φ due to bulk quenching and at higher φ due to excessive stratification. The combustion efficiency estimated from combustion products shows good agreement with that of heat release analysis(Fig. 12). Thus CNG DI is considered to have much potential to be used in a spark-ignition engine from the point of view of these beneficial characteristics of wide operation range and possibly high energy conversion efficiency.