Hybrid internal combustion engine : driving a vehicle using air compressed in braking

Abstract

After the oil crisis of the 1970's, stringent government standards placed on automobile manufacturers have led the industry to explore more fuel efficient alternatives to the vehicle with a conventional internal combustion engine/transmission powertrain. This is the motivation behind Mr. David F. Moyer's hybrid internal combustion engine concept. A vehicle using this engine should attain higher fuel economy levels as a result of kinetic energy recovery and reuse (achieved by using the engine as an air compressor during braking, storing the compressed air, and then utilizing that air to turn the engine and drive the vehicle), cylinder disabling, and the elimination of idling losses. Data of transmission input power for Ford Motor Company's P2000 vehicle while driven through 1373 seconds of typical urban driving (CVS cycle) were used, combined with a model to estimate engine friction, to carry out an available energy analysis of the hybrid engine. An air processing efficiency was incorporated into the analysis to determine how irreversible the air storage/use processes were. Fuel economy was estimated for the different operating conditions of the concept by matching Ford's 1.8-litre Zetec engine to the vehicle and using the fuel consumption map for that engine. The vehicle with the baseline engine yields 32.6 mpg. Adding cylinder disabling raises this value to 36.8 mpg. Ultimately, if reversible hybrid operation is added, the best possible fuel economy this concept can achieve is 52.4 mpg, for a total maximum savings of 38% in fuel consumption. Using simple thermodynamic models of a braking and an air driving event, we predicted maximum values of 85% and 88% for the air processing efficiency in the braking and the air driving case, respectively. An overall value of 65% was chosen for the efficiency, resulting in a maximum fuel economy of 48.1 mpg and fuel savings of 32%. The analysis above led us to conclude that engine friction plays a significant role in reducing the benefit of this hybrid concept. Furthermore, fully variable valve timing and cylinder disabling improve fuel economy for a conventional engine significantly, and they are essential in minimizing the thermodynamic losses involved in hybrid operation. Therefore, we recommend that methods to reduce engine friction as well as means to implement fully variable valve timing modifications to an internal combustion engine be explored further.