Impact of ignition energy on the combustion performance of an SI heavy-duty stoichiometric operation natural gas engine

Abstract

Nowadays, natural gas engine has been brought opportunities because of its low C/H ratio. For the stoichiometric combustion natural gas engine, improving its combustion stability is the main challenge under the condition of high EGR rate. To better understand the effect of the ignition energy on combustion stability, a detailed study was conducted by experiment. A 6-cylinder turbocharged intercooler natural gas heavy-duty engine was used in this study, and the ignition energy was controlled over a wide range under different working conditions. The results show that the ignition energy has an obvious effect on the ignition process of combustion including flame inception and early development when exceeds 100 mJ. Under heavy-load conditions, the elevating of early combustion speed can shorten the duration of combustion (DOC), manifesting more concentrated heat release, and improve the combustion stability and economy of the engine. However, under light-load conditions, the increase of early flame speed has little impact on the subsequent combustion process, and engine performance is not significantly improved. For a specific ignition energy under 1200r/min-80% load working condition, with the advancing of ignition timing (IT), there is a little effect on ignition delay time (IDT), but has more obvious effect on DOC. What’s more, the improvement amplitude of Pmax and indicated mean effective pressure (IMEP) gradually decrease with the advancing of IT at 105 mJ, but they are still larger than at 150 mJ. Overall, better engine performance and thermal efficiency can be achieved by organizing ignition energy.