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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.

Air-fuel ratio (AFR) is a crucial parameter for combustion controls in internal combustion engines. An incorrect AFR metering for reciprocating internal combustion engine causes high toxic gases emissions formulation, serious fuel consumption problems and unbearable combustion noise and combustion deterioration. Traditionally, the AFR is obtained by direct measurement of intake air and the fuel either injected into the combustion chamber or pre-mixed at the carburetor. However, the accurate AFR obtained from direct measurement is difficult due to measuring equipments resolution prone to errors. This paper describes a method for accurate determination of air-fuel ratio based on exhaust emission gas analysis as an additional tool used to be validated the conventional direct air fuel flow rates measurement.

This research work focuses on the unsteady heat transfer and temperature distribution over the engine cooling jackets. The efforts are gestated to generate the time-dependent effects of heat transfer from the combustion chamber to the cooling jacket of a 4-cylinder 1.6-L cam-profile switching system SI engine. The characteristic behavior of heat transfer to the coolant at lower speed (idle speed/traffic signal) or when the engine is shut down after driving the vehicle for a significant period manifests unstable temperature rise with respect to time. It has been observed that the temperature of the coolant inside the jacket rises up within a very short period of time. It can be a case due to the shut off of the actuators (coolant pump, fan) which helps the cooling system to take effect according to the demand of the thermal efficiency of the engine.