Effect of n-butanol additive on the combustion and emission characteristics of a coal-derived naphtha homogeneous charge compression ignition engine under different parameters

Abstract

ABSTRACT The combustion and emission characteristics of n-butanol/coal-derived naphtha blends in homogeneous charge compression ignition (HCCI) combustion mode were experimentally researched on a retrofitted diesel engine. The effects of intake temperature (T in ) and excess-air coefficient (λ) were mainly analyzed. The results show that the peak in-cylinder pressure (P max ) and peak heat release rate (HRR max ) of all tested fuels show an overall increasing trend as T in rises. The combustion gets faster and more stable, carbon monoxide (CO) and hydrocarbon (HC) emissions decrease, and the indicated thermal efficiency (ITE) first increases and then decreases. When T in remains constant, the P max and HRR max decrease and the combustion phase delays as the n-butanol volume fraction increases; CO and HC emissions gradually increase, except for that of lower T in , which shows a trend of first reduction and then increase. ITE gradually decreases in general, but when T in is higher than 100°C, coal-derived naphtha containing 24% of n-butanol in volume (B24N76) exhibits the highest ITE. In addition, for all tested fuels, both P max and HRR max decrease as λ increases and the combustion gets slower and less stable; CO and HC emissions deteriorate, and ITE gradually decreases. It is worth noting that B24N76 shows the best combustion stability for all λs and exhibits the lowest CO and HC emissions when λ are 3.0 and 3.5.