Investigation of Fuel Injection Strategies for Direct Injection of Neat n-Butanol in a Compression Ignition Engine

In this study, impacts of neat n-butanol fuel injection parameters on direct injection (DI) compression ignition (CI) engine performance were investigated to gain knowledge for understanding the fuel injection strategies for n-butanol. The engine tests were conducted on a four-stroke single-cylinder DI CI engine with a compression ratio of 18.2:1. The effects of fuel injection pressure (40, 60 and 90 MPa) and injection timing in a single injection strategy were investigated. The results showed that an increase in injection pressure significantly reduced nitrogen oxides (NOx) emissions which is the opposite trend seen in conventional diesel combustion. The parallel use of a higher injection pressure and retarded injection timing was a proposed method to reduce NOx and cylinder pressure rise rate simultaneously. NOx was further reduced by using exhaust gas recirculation (EGR) while keeping near zero soot emissions. However, the high load limit was around 6.5 bar indicated mean effective pressure (IMEP) due to high cylinder pressure rise rate. Next, the effect of a split injection, in which the fuel delivery is divided into two injections (first and second injection ratio: 50:50) near top dead center, on the engine performance was investigated to reduce the cylinder pressure rise rate. The split injection could significantly reduce the cylinder pressure rise rate without compromising the indicated thermal efficiency, NOx and soot emissions. It was also demonstrated that the high load limit could be extended to 11.5 bar IMEP by modifying the split injection ratio while maintaining high thermal efficiency and clean emissions.