Mixture formation and ignition in a direct injection natural gas engine

Abstract

A natural gas fueled direct injection test engine, equipped with a newly developed natural gas injector, was designed and the influences of injection timing and spark timing on indicated mean effective pressure and exhaust emissions were investigated. The following results were obtained: (1) The location of the spark plug relative to the injection nozzle location and the piston cavity wall needs to be optimized to achieve a wide range of stable ignition and engine operating conditions; (2) Impingement of the gas jet against the cavity wall and high injection pressure are two key factors required to control ignition and combustion of the gas jet; (3) In terms of-mixture preparation around the spark plug, early injection is preferable at low load conditions, and late injection at high load conditions; (4) When excess air ratio λ is 1.06 and 1.4, THC concentration was about 1 000 ppm and NOx concentration exceeds 1 000 ppm. When λ values are 2 and 2.3, THC concentration was high but NOx concentration was below 100 ppm.