Effect of Two-Stage Injection Timing on a Gas-Jet Ignition CNG Engine

Abstract

Compressed natural gas (CNG) engines normally operate in lean condition to take the advantage of higher efficiency and better fuel economy. Several studies have shown that gas-jet ignition with two-stage injection technique is effective to extend the lean combustible range of CNG engines. This paper investigates the effectiveness of such technique using a prototype lean burn direct injection CNG engine. The experiment was conducted at speed of 900 rpm, fuel injection pressure of 3 MPa, equivalence ratio φ=0.8, and ignition timing at top dead center. The effect of first injection timing on the test engine performance and exhaust emission was analyzed. The result shows that the first injection timing is crucial in determining the performance of the engine. First injection timings when the piston is near to bottom dead center produced relatively stable combustion. First injection timings when the piston is at midpoint produced misfire. First injection timings near the gas-jet ignition produced unstable combustion except at a certain timings which produced acceptable combustion with low hydrocarbon and carbon monoxide emissions.