Study on the effect of injection strategy on the combustion and emission characteristics of direct injection spark ignition bio-butanol engine

Owing to its physicochemical similarities with gasoline and renewable nature, n-butanol (bio-butanol) has garnered significant researcher interest. However, the lower atomization and volatility of n-butanol pose challenges when implemented in direct-injection spark-ignition (DISI) engines, leading to inhomogeneous air-fuel mixtures which subsequently results in a deterioration of combustion performance and an uptick in pollutant emissions. This study uses numerical simulations to examine the effects of injection pressure and timing on mixture formation, combustion, and emission characteristics in n-butanol DISI engines. The results indicate that for n-butanol, characterized by its reduced volatility and atomization capabilities, enhancing injection pressure from 10 MPa to 20 MPa effectively improves combustion and emission performance. However, the benefits taper off with subsequent increases in pressure. At injection pressure of 20 MPa, optimizing injection timing offers better combustion and emission results than merely increasing injection pressure. An early injection, represented by −300°CA start of injection, provides extended evaporation and mixture diffusion, significantly improving mixture quality and resulting in better combustion and emission outcomes. At −260°CA start of injection, while peak in-cylinder pressures can be achieved more favorably, the resultant inhomogeneous in mixture distribution results in increased emissions of CO, soot, and HC.