Abstract
The diesel engine converted to compressed natural gas (CNG) engine effect is lower in performance. Problem statement: The hypothesis is that the lower performance of CNG engine is caused by the effect of lower in engine cylinder pressure. Are the CNG engine is lower cylinder pressure than diesel engine? This research is conducted to investigate the cylinder pressure of CNG engine as a new engine compared to diesel engine as a baseline engine. Approach: The research approach in this study is by convert the diesel engine to multi point injection dedicated CNG engine. The engine conversion is by changed the diesel fuel to CNG fuel, changed the injection fuel system, changed the ignition system, modified piston to reduce the compression ratio and added throttle to in intake port. If the development is completed, the engine cylinder pressure is investigated. In this study, the cylinder pressure is investigated in 7 cases engine speed from 1000 to 4000 rpm with range in 500. Results: The research results are cylinder pressure and maximum pressure of CNG engine compared to diesel engine in 1000 to 4000 rpm engine speed. Conclusion/Recommendations: Effect of diesel engine converted to CNG engine is decrease the cylinder pressure. The further research is needed to find the higher performance of CNG engine.
Highlights
The compressed natural gas (CNG) engine is lower performance compare to diesel
The engine cylinder pressure profile investigation results are shown that, the cylinder pressure is increasing in compression stroke to ignition in crank angle-180 degree (BDC) until around in crank angle 0 degree (TDCF)
In all of engine speeds from 1000-4000 rpm are shown that the diesel engine cylinder pressure is higher than the CNG engine
Summary
The CNG engine is lower performance compare to diesel. The range for CNG engine is typically limited to about 40%-50% of gasoline fueled engine[1]. Values as much as 60% decrease in lower burning velocity for natural gas has been measured[3] This effect on the total combustion duration is prolonged compared with diesel and gasoline. With the conventional valve timing setting for liquid fuel engines, it would be impossible for CNG operation to complete the whole combustion before the exhaust valve opens, even if the gas mixture was ignited earlier. This can cause a further reduction in the engine output of 5-10%. Absence of fuel evaporation of CNG engine is when gasoline evaporates (required before combustion), the energy required for the phase change decrease intake charge temperature and air partial pressure[4,5].
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