A numerical study of the use of pilot or split rate injection to reduce diesel engine noise

This paper investigates the effects of the various factors on combustion noise without increasing nitrogen oxides (NOx) in different operating conditions, especially at idle by using a combustion-simulation computer program (KIVA) and orthogonal array. Results indicated that the effects of pilot or split injection, compression ratio, and dynamic injection timing on combustion noise were strong at idle, while the effects of induction swirl ratio and number of injector holes were weak. Injection rate shaping, pilot or split injection, and double injections showed promising reduction in combustion noise and NOx simultaneously at the idle condition. The selected optimized injector (a split injection) for combustion noise reduction at the idle engine operating condition created different rate shapings from the baseline engine at medium speed and full load. This injector lowered combustion noise and NOx at medium speed and full load in comparison with the baseline injector. Generally, the pilot or split injection and double split injections are beneficial to reduce combustion noise and NOx at idle. Their effects are reduced as engine speed and load are increased such that no significant reduction in combustion noise occurs at high speeds and high loads.