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Modelling engine and exhaust temperatures of a mono-fuelled turbocharged compressed-natural-gas engine during warm-up

Abstract A promising way to reduce the carbon dioxide emissions of vehicles is the use of engines fuelled only by compressed natural gas (CNG). However, even with CNG, restrictions on pollutants such as methane and non-methane hydrocarbons must be complied with. In a modern spark ignition (SI) engine, most of the pollutants are produced during the cold start before the catalytic converter reaches its light-off temperature. To avoid costly problems late in the development phase, it is reasonable to assess the functionality of the exhaust system as a whole, and the light-off behaviour of the catalytic converter in particular, as early as possible using simulation. Today's state-of-the-art catalytic converter simulation tools require the temperature signal upstream of the catalytic converter as input. This necessitates an easily applicable simulation tool of the exhaust temperature that takes the engine warm-up into account. This paper presents a new physics-based model for the estimation of the engine and exhaust temperatures for a CNG-fuelled SI engine during warm-up. A new mean value model for the combustion wall heat transfer and also a lumped-parameter consideration of the cooling fluid are presented. In addition, existing methods for engine modelling are adapted to account for engine warm-up. Based on measurements performed on a special test bench assembly, the most important physical effects occurring in this phase are identified. Various experiments for parameterization and validation of the model are carried out. Tests for all relevant engine operating variations confirm a good correlation between the model and measurement results.