Numerical investigation for enhancing HCCI combustion characteristics in DI-CI engine fueled with butanol/diesel blends

The fast depletion of fossil fuels and the hazardous emissions associated with the use of fossil fuels in IC engines is driving the research in the area of renewable fuels. Homogeneous charge combustion ignition (HCCI) is a new mode of engine combustion technology, used for reducing the emissions without compromising the engine performance. The combination of HCCI and alcohol/diesel blends has the potential to simultaneously address the twin problems of depletion of fossil fuels and engine emissions. Butanol is an attractive biofuel, which is produced from agriculture wastes such as sugar cane bagasses and corn stalk etc. This paper presents numerical and modeling analysis on the emission and performance characteristics of a direct injection- compression ignition (DI-CI) engine operated with butanol/diesel blends. Numerical analysis was carried out using CONVERGE CFD software. Response surface methodology (RSM) was used in developing the response models for three output parameters, viz., nitrogen oxides (NOx), soot emissions and indicated specific fuel consumption (ISFC), in terms of the four input parameters, viz., compression ratio (CR), start of injection (SOI), fuel injection pressure (FIP) and exhaust gas recirculation (EGR). Numerical experiments were conducted by varying these four input parameters, i.e., CR from 14 to 19, FIP from 200 to 280 bar, EGR from 0% to 30% and SOI from 17° to 29° CA bTDC, and with four butanol/diesel blends (0, 20%, 30% and 40% of butanol-by volume, designated as Bu00, Bu20, Bu30 and Bu40). The optimum combination of the input parameters for the four test fuels were found with the objective of minimizing the three output parameters (i.e., ISFC, soot and NO_x) using desirability approach. The homogeneity of the air-fuel mixture was estimated using equivalence ratio distribution index, i.e., Target fuel distribution index (TFDI). From the numerical analysis, it was found that the TFDI improved for the optimized case by 20.5%, 21.5%, 24.4% and 27.2% for Bu00, Bu20, Bu30 and Bu40 respectively as compared to their respective baseline configuration.