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This paper presents exhaust gas emissions characteristcs of a new direct injection (DI) compressed natural gas (CNG) engine using a low cost catalytic conveter (Catco). The pollutants exhaust gas emissions measured were CO, HC and NOx with and without Catco. The Catco was developed based on catalyst materials consisting of metal oxides such as titanium dioxide (TiO2) and cobalt oxide (CoO) with wiremesh substrate. Both of the catalyst materials (such as TiO2 and CoO) are inexpensive in comparison to conventional catalysts (noble metals) such as palladium or platinum. In addition, the noble metals such as platinum group metal are now indentified as human health risk due to their rapid emissions in the environment from various resources like conventional catalytic converter, jewelers and other medical usages. It can be mentioned that both the CNG-DI engine and TiO2/CoO based catalytic converter were developed under a research collaboration program.

This paper presents experimental test results of a new compressed natural gas direct injection (CNG-DI) engine that has been developed from modification of a multi cylinder gasoline port injection (PI) engine. The major modifications done are (1) the injection system has been modified to gas direct injection using new high pressure gas injectors, (2) compression ratio has been changed from 10 to 14 through modification of piston and cylinder head, and (3) new spark plugs with long edge were used to ignite the CNG fuel. The CNG pressure at common rail was kept at 20 bar to be injected into engine cylinder. The engine has been operated with full throttle conditions to compare all the results with original base engine such as gasoline port injection engine and the CNG bi-fuel engine where the base engine has been converted to bi-fuel injection system to be operated with gasoline and CNG fuels.