This study investigated neat n-butanol combustion, emissions and thermal efficiency characteristics in a compression ignition (CI) engine by using two fuelling techniques - port fuel injection (PFI) and direct injection (DI). Diesel fuel was used in this research for reference. The engine tests were conducted on a single-cylinder four-stroke DI diesel engine with a compression ratio of 18.2 : 1. An n-Butanol PFI system was installed to study the combustion characteristics of Homogeneous Charge Compression Ignition (HCCI). A common-rail fuel injection system was used to conduct the DI tests with n-butanol and diesel. 90 MPa injection pressure was used for the DI tests. The engine was run at 1500 rpm. The intake boost pressure, engine load, exhaust gas recirculation (EGR) ratio, and DI timing were independently controlled to investigate the engine performance.
The pressure rise rate of the DI could be lowered easily by retarding the injection timing without using EGR, whereas a very high EGR ratio was required for the PFI to reduce the pressure rise rate to the same level of the DI. Soot and nitrogen oxides (NOx) emissions for both fuelling techniques were at a very low level compared to those of base diesel, but the NOx for DI was slightly higher than that for PFI at 0% EGR. However, by using EGR, NOx was reduced to around 20 ppm, similar to the PFI level. Indicated thermal efficiency of the DI was greater than that of the PFI with the same NOx and cylinder pressure rise rate.
