Compression Ignition of Light Naphtha and Its Multicomponent Surrogate under Partially Premixed Conditions

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. The low temperature reaction (LTR) phase exhibited by LN and its surrogate were comparable, while ignition delay was prolonged as SOI is advanced from CI to HCCI combustion. Combustion images for LN and its surrogate were nearly similar, showing equal behaviour in both fuels. The level of stratification estimated from the intensity of the images was comparable between LN and its surrogate at various SOI. Stratification analysis showed stratified combustion, and the decay of stratification was slower under PPC conditions than under CI conditions. Emissions such as nitrogen oxide (NO_X), carbon monoxide (CO) and soot concentration were comparable for the real and surrogate fuels. Overall, this study demonstrates that the surrogate resembles its real fuel (LN) under the current set of engine test conditions.