Numerical Investigation on Effects of Assigned EGR Stratification on a Heavy Duty Diesel Engine with Two-Stage Fuel Injection

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Abstract
External exhaust gas recirculation (EGR) stratification in diesel engines contributes to reduction of toxic emissions. Weak EGR stratification lies in that strong turbulence and mixing between EGR and intake air by current introduction strategies of EGR. For understanding of ideal EGR stratification combustion, EGR was assigned radically at −30 °CA after top dead center (ATDC) to organize strong EGR stratification using computational fluid dynamics (CFD). The effects of assigned EGR stratification on diesel performance and emissions are discussed in this paper. Although nitric oxides (NOx) and soot emissions are both reduced by means of EGR stratification compared to uniform EGR, the trade-off between NOx and soot still exists under the condition of arranged EGR stratification with different fuel injection strategies. A deterioration of soot emissions was observed when the interval between main and post fuel injection increased, while NO emissions increased first then reduced. The case with a 4 °CA interval between main and post fuel injection is suitable for acceptable NO and soot emissions. Starting the main fuel injection too early and too late is not acceptable, which results in high NO emissions and high soot emissions respectively. The start of the main fuel injection −10 °CA ATDC is suitable.
Funding Information
  • National Natural Science Foundation of China (51606052, 51506038)
  • China Postdoctoral Science Foundation funded project (2016T90284, 2015M571411)
  • Weihai Science and Technical Plan Project (2016DXGJMS10)
  • he Scientific Research Foundation of the Harbin Institute of Technology at Weihai, (WH20160104)
  • Natural Scientific Research Innovation Foundation at the Harbin Institute of Technologynical Plan Project (HIT.NSRIF.2016095)

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