SAE International Combustion Stratification with Partially Premixed Combustion, PPC, using NVO and Split Injection in a LD - Diesel Engine 2014-01-2677

Partially Premixed Combustion (PPC) is used to meet the increasing demands of emission legislation and to improve fuel efficiency. PPC with gasoline fuels have the advantage of a longer premixed duration of fuel/air mixture which prevents soot formation at higher loads. The objective of this paper is to investigate the degree of stratification for low load (towards idle) engine conditions using different injection strategies and negative valve overlap (NVO). The question is, how homogenous or stratified is the partially premixed combustion (PPC) for a given setting of NVO and fuel injection strategy. In this work PRF 55 has been used as PPC fuel. The experimental engine is a light duty (LD) diesel engine that has been modified to single cylinder operation to provide optical access into the combustion chamber, equipped with a fully variable valve train system. Hot residual gases were trapped by using NVO to dilute the cylinder mixture. Optical measurements were carried out for OH chemiluminescence imaging to track sequentially the combustion process and to analyse the degree of stratification. Initial results show that the combustion with triple injection is more homogenous compared to single and double injection. Furthermore the results show that the 55 octane number fuel can be operated at low load condition with the lowest NVO used, 60 CAD.