Abstract
Implementation of natural gas in transportation sector is increasing along with an experience of loss in engine power. Direct injection (DI) compressed natural gas (CNG) engine has become an alternative to solve this drawback by increasing the volumetric efficiency of the engine. Injection parameter such as injection timing has proven to be able to increase the performance of a DICNG engine that has been done in the previous report. While other injection parameter such as injection spray angle in DI-CNG engine has yet to be reported. Thus, variation of the injector spray angle in a compressed natural gas (CNG) direct injection (DI) engine is done in a single cylinder engine. This engine is designed with a compression ratio of 14 and equipped with central DI system. Two high pressure injectors are employed; wide angle injector (WAI) with 70° and narrow angle injector (NAI) with 30° spray angles respectively. Each injector is examined at two injection timings, early injection timing at 300°BTDC to simulate port injection and late injection timing as a direct injection method at 140° BTDC. Experiments are done at stoichiometric conditions with engine speeds varying in the range of 2000 RPM to 5000 RPM. The results show that each injector spray angle gives optimum performance at specific engine operation due to its mixture characteristics. NAI shows better performance at low engine speeds while WAI at higher engine speeds for both injection timings. Furthermore, early injection timing has significant performance difference with variation of injector spray angles compared to late injection timing. Exhaust emissions for late injection timing are showing significant difference especially at engine speeds below 3000 RPM. NAI has lower values for HC and CO emission and higher value for NOx compared to WAI that shows better combustion occurs with NAI injector. It may occur due to higher stratification with NAI at lower engine speed. However, the emissions difference between the two injector spray angles getting smaller as the engine speed increases showing that the mixing capability for injectors is quite similar at high engine speeds. It also shows that the injector spray angles have less effect in the mixing process at high engine speed with late injection timing.
Keywords: Compressed Natural Gas -CNG, Direct Injection- DI, Injector spray angle, Homogeneous, Stoichiometric.