Theoretical and experimental evaluation of performance of CNG engine and pistons fatigue lives employing modified fatigue criteria

Abstract

In the present paper, a systematic procedure for theoretically evaluating performance and relevant fatigue failure of the pistons is presented and validated by engine test results. The proposed procedure includes modeling of the combustion, heat transfer, kinematic and dynamics analyses of the moving parts of the engine, transient thermoelastic analysis, and fatigue failure analysis under the complex thermomechanical loading conditions. The predicted pressure and temperature versus crank angle curves show a good agreement with the experimental results. The heat transfer results are validated by the experimental results measured by the Templugs. The moving system is assumed to be a continuous system rather than a discrete system and the nonlinear multipoint contact constraints are modeled accurately. Modified critical plane-type McDiarmid’s and Findley’s high-cycle fatigue criteria recently proposed by the first author are also evaluated and validated by the present experimental durability tests. The presented procedure may be used to decide whether it is suitable to convert a gasoline-based engine to a CNG one. Results of the various thermomechanical fatigue analyses performed confirm the accuracy of the recently proposed fatigue criteria and reveal that the piston life decreases considerably when natural gas is used instead of gasoline.