The effect of engine throttle position on the performance characteristics of a crank-rocker engine fitted with a conventional cylinder head

This paper presents the investigation on the effects of throttle position variations on the performance characteristics of a single-piston curved-cylinder four-stroke SI Crank-Rocker (CR) engine fitted with a conventional engine cylinder head. The CR engine is a new alternative IC engine for which the performance characteristics are still being investigated. All of the experiments were conducted at an engine speed of 2000 rpm with the ignition timing set at 6.5° CA BTDC. The throttle position, or the load, was varied from 25% to 100%. The best engine performance was found to be at the 75% throttle position where the torque, power, and thermal efficiency were at the maximum values of 4.16 Nm, 0.87 kW, and 18%, respectively, whilst the brake specific fuel consumption was at the minimum amount of 423 g/kw-h. All of the result trends for emissions of CO, NO_X, and Unburned Hydrocarbon (HC) were found to be in-line with conventional engines up to 75% throttle position. For the loads higher than 75%, the CR engine behaved the opposite to the emission characteristics of the conventional engines. The reason behind the inverse behaviour of the CR engine after the 75% load was due to the `choke' phenomena at the intake valve. The study revealed that larger inlet ports are required for further improvement of this engine's performance. The results are advantageous in comparing the performance and designing the parameters of the CR engine with a conventional engine having the same capacity.