Experimental investigation the effects of spark discharge characteristics on the heavy-duty spark ignition natural gas engine at low load condition

The fuel economy of natural gas (NG) spark ignition (SI) engine could improve significantly when using high exhaust gas recirculation (EGR) dilution. However, the combustion processes become instability and even occur misfire at higher EGR rate. In this paper, the high energy ignition system, which was the technology of variable spark, was utilized to extend the EGR tolerance of a SI engine. Extensive experimental tests were conducted to investigate the effects of spark discharge current and duration on combustion and emissions characteristics at low load condition. The results showed that the fuel economy was improved with the spark discharge energy at the high EGR rate of 30%. The increase amplitude of fuel economy was 1.32% when the spark discharge energy increased from 210 to 320 mJ. The effective spark discharge energy was existed in consideration of the fuel economy. The ignition delay (CA0-5) and the flame propagation period (CA10-90) shortened with an increase in spark discharge energy. Besides, NOx emissions were more sensitive to the spark discharge energy than that of HC and CO emissions. As the spark discharge energy increased, the increase extent of NOx emissions was 26.9%, while HC and CO emissions decrease slightly.