소형 직분식 디젤엔진에서 다공분사기를 이용한 파일럿 분사와 배기가스 재순환의 영향

Abstract

The effect of multi-hole injector, EGR and pilot injection is studied on the purpose of reducing the particulate matter (PM) and nitrogen oxides (NOx) emissions in a high speed direct-injection (!-ISOI) diesel engine. Multi-hole injector could lead faster atomization and vaporization due to the small hole-diameter. It increases the portion of the premixed combustion, which results in low PM emission. Adversely, NOx emission increases due to the rise of the combustion temperature with enhancement of the air-fuel mixing. EGR could be applied to resolve this problem. In addition, pilot injection could compensate power output and assist NOx reduction. The main objective of this study is to investigate the effects of the combined use ofEGR and optimized pilot injections with multi-hole injector on combustion and emissions. The study was carried out in a single-cylinder optical direct-injection (01) diesel engine equipped with a high pressure commonrail fuel injection system Tests were performed at fixed engine speed (800 rpm) with variations of the EGR rate and the il*ction pressure. Two different injectors with 5 and 14 holes were tested. EGR rate was applied trom a % to 50 %, and pilot injection test was perfom1ed under the same condition. The experimental results showed that 14-hole injector achieved better combustion performance, while it increased NOx emission at 60 MPa injection pressure. EGR reduced NOx emission by 80-90 % without a significant increase in PM emission. The reduction of flame lun1inosity through the visualized combustion explained these phenomena. The optimized use of multihole injector, EGR and pilot injection showed the in1proved power output and the reduced NOx and PM emissions.