Principle of valves timing optimization in D87 diesel to premixed natural gas engine conversion

In recent years, heavy duty engine manufacturers have increased natural gas engine products to be used especially due to its potential in offering lower fuel cost, lower NOx emission and gas-fuel worldwide availability. Through D87 diesel to gas conversion project, to achieve minimum thermal efficiency of 35% at phase 1 and 42% in final phase, use of mixer in upstream of compressor was prioritized to other prevalent strategies for fuel and air mixing. This study has been investigated under scope of phase 1 of the project (minimum thermal efficiency 35%). Therefore, with this mixing strategy, since air stream is replaced with air-fuel mixture in engine suction chest, primary studies have shown that valve’s timing plays significant role to achieve project’s target. Hence, after approving the lack of diesel base valve timing in achieving the minimum thermal efficiency, investigating exhaust and intake valves timing effect has come up with this result that intake and exhaust valves overlap has the prominent effect in scavenging which consequently has resulted in overlap reduction from 110 CAD degrees in diesel engine to 33 CAD degrees in natural gas engine. Finally, natural gas engine test results which represent 38% brake thermal efficiency are compared with simulation final predicted results.