Search Results

Partially premixed combustion (PPC) is a low-temperature combustion concept, which is between conventional diesel compression ignition (CI) and homogeneous charge compression ignition (HCCI). In PPC mode, the start of injection timing (SOI) is earlier than that of CI and later than that of HCCI and stratified in-cylinder fuel/air mixture can be formed to control the auto-ignition by the fuel injection timing. Gasoline fuel is beneficial for PPC mode because of its superior resistance to auto-ignition, which can enhance fuel-air charge mixing process with longer ignition delay time. The scope of this study is to investigate in-cylinder auto-ignition, combustion evolution, combustion stratification, and engine-out emissions at PPC operating mode under lean and low load engine conditions with different injection timings. Primary reference fuel PRF77, was selected as the low-octane test fuel.

In the engine community, gasoline compression ignition (GCI) engines are at the forefront of research and efforts are being taken to commercialize an optimized GCI engine in the near future. GCI engines are operated typically at Partially Premixed Combustion (PPC) mode as it offers better control of combustion with improved combustion stability. While the transition in combustion homogeneity from convectional Compression Ignition (CI) to Homogenized Charge Compression Ignition (HCCI) combustion via PPC has been comprehensively investigated, the physical and chemical effects of fuel on GCI are rarely reported at different combustion modes. Therefore, in this study, the effect of physical and chemical properties of fuels on GCI is investigated. In-order to investigate the reported problem, low octane gasoline fuels with same RON = 70 but different physical properties and sensitivity (S) are chosen.

Partially premixed combustion (PPC) is an operating mode that lies between the conventional compression ignition (CI) mode and homogeneous charge compression ignition (HCCI) mode. The combustion in this mixed mode is complex as it is neither diffusion-controlled (CI mode) nor governed solely by chemical kinetics (HCCI mode). In this study, CFD simulations were performed to evaluate flame index, which distinguishes between zones having a premixed flame and non-premixed flame. Experiments performed in the optical engine supplied data to validate the model. In order to realize PPC, the start of injection (SOI) was fixed at −40 CAD (aTDC) so that a required ignition delay is created to premix air/fuel mixture. The reference operating point was selected to be with 3 bar IMEP and 1200 rpm. Naphtha with a RON of 77 and its corresponding PRF surrogate were tested. The simulations captured the general trends observed in the experiments well.

Light naphtha is the light distillate from crude oil and can be used in compression ignition (CI) engines; its low boiling point and octane rating (RON = 64.5) enable adequate premixing. This study investigates the combustion characteristics of light naphtha (LN) and its multicomponent surrogate under various start of injection (SOI) conditions. LN and a five-component surrogate for LN, comprised of 43% n-pentane, 12% n-heptane, 10% 2-methylhexane, 25% iso-pentane and 10% cyclo-pentane, has been tested in a single cylinder optical diesel engine. The transition in combustion homogeneity from CI combustion to homogenized charge compression ignition (HCCI) combustion was then compared between LN and its surrogate. The engine experimental results showed good agreement in combustion phasing, ignition delay, start of combustion, in-cylinder pressure and rate of heat release between LN and its surrogate.