Energy Efficiency Improvement Adding Various Amounts of CNG in the Naturally Aspirated Compression Ignition Engine

The work is devoted to improve energy efficiency and environmental indicators of compression-ignition indirect injection (IDI) engines of transport means and small scale energy sectors, by decreasing dependence on conventional diesel oil by adding compressed natural gas (CNG) in dual fuel mode. It was found that the addition of CNG affects positively on combustion process thermal efficiency and negatively influence on incomplete combustion products such as hydrocarbons (HC) which in average increases from 0 ppm to 320 ppm. Carbon monoxide (CO) in average increase by about 70% on high and about 90% on medium and low loads comparing with diesel fuel mode. Carbon dioxide (CO2) emissions decrease in average 7%. The nitrogen oxides (NOx) emissions results are controversial, because in higher load modes with dual fuel mode it increased comparing with diesel fuel mode but during low and medium load it decreases sufficiently. Energy efficiency in dual fuel mode during all loads determined higher in high load with all dual fuel mixtures comparing with pure diesel combustion mode, but in medium and low loads because of 25% decrease in excess air ratio the brake specific fuel consumption (BSFC) increases from 7-15% comparing with diesel fuel. The aim of the research is to improve fuel economy and reduce conventional diesel consumption of old low power diesel engine by adding a compressed natural gas in to the combustion process.