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Wear of piston ring and cylinder was modelled through a computer code that calculates the hydrodynamic and roughness contact pressures acting on the contact surfaces. Both pressures are fully and coupled solved through, respectively, Reynolds equation and Greenwood-Williamson model. Piston secondary motion and piston groove thermal deformations are considered. The latter was discovered to be fundamental in defining the top ring worn profile. Due to the rough contact pressures, the model predicts material removal from both piston ring and cylinder surfaces and recalculates the system, hence simulating the evolution of the worn sliding surface of both parts. The predicted wear of the piston ring pack and the cylinder wall are compared with a medium duty diesel engine tested for 750 hours in dynamometer.

As standards for hydrocarbon emissions from vehicles become more stringent due to environmental concerns, considerable effort has been devoted to investigate the mechanisms of formation, transport, and oxidation of unburned hydrocarbons in spark ignition engines. In order to understand controlling factors in the processes, a transient one-dimensional reactive-diffusive model has been formulated for simulating the oxidation process taking place in the reactive layer between hot burned gases and cold unreacted air-fuel mixture, and for estimating exhaust hydrocarbon emission levels from natural gas spark ignition engines. The main innovation shown by the model is the consideration also of the expansion of crevice gas in the axial direction. The model takes into consideration the contribution of the top land piston-ring crevice phenomenon, this being the main unburned hydrocarbon source in natural gas engines.

Aiming at evaluating the effects of natural gas composition on engine operation, the Engine Group of IPT has completed a series of dynamometer tests in a Mercedes Benz M366G gas engine. Twenty-five gaseous fuel compositions, several specially prepared to extend the available CNG compositions, were engine tested. The tests were executed to evaluate performance, exhaust emissions and knock-limited spark timing. The experimental results were correlated with methane and Wobbe numbers calculated from the gas composition. The obtained data corroborate the relevance of these parameters to engine operation. For the tested engine, that uses an open loop fuel system, the data indicate the need to maintain the natural gas specifications in narrow limits if one wants to explore the natural gas low pollutant potential. This study has subsidized the elaboration of a Brazilian vehicular natural gas specification.