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Technical Paper

Spark–Ignition Engine Fuel Consumption Modeling

An analytical model that describes SI engine fuel consumption and friction with basic engine physical parameters as inputs has been developed and evaluated in this study. Fundamental characteristics of SI engine indicated efficiency, heat loss and friction have been captured by the model. Despite the approximations made in arriving at the final formula of the model, the proposed fuel–rate equation has been shown to represent both the SI engine fuel consumption and WOT friction reasonably well with a base set of parameters. If both the engine performance data and motored WOT friction data are available, the proposed model can be used to obtain a more precise set of parameters that describe both the engine friction and fuel consumption accurately (fuel rate differences within ±5%) at any speed and load combinations (omitting enrichment points).
Technical Paper

Modeling of Direct Injection Diesel Engine Fuel Consumption

Due to their inherent high efficiency and the ease of starting once the engine is hot, turbocharged direct injection (TDI) diesel engines have emerged as one of the contending powerplants for PNGV hybrid vehicles. The interest in applying diesel engines in hybrid vehicles has prompted the modeling of direct injection diesel engine fuel consumption. The empirical equation developed in this study, which models engine friction and indicated efficiency as functions of engine operating speed and load, shows excellent agreement with test data gathered from public sources. The engine speed dependence of the friction and indicated efficiency are determined by fitting available data. Several assumed load dependences are considered. (If public data were available on engine cylinder pressure by crank angle as a function of engine speed and load, the load dependence could be determined empirically.)