Browse Publications Technical Papers 2020-01-0797
2020-04-14

Isobaric combustion at a low compression ratio 2020-01-0797

In a previous study, it was shown that isobaric combustion cycle, achieved by multiple injection strategy, is more favorable than conventional diesel cycle for the double compression expansion engine (DCEE) concept. In spite of lower effective expansion ratio, the indicated efficiencies of isobaric cycles were approximately equal to those of a conventional diesel cycle. Isobaric cycles had lower heat transfer losses and higher exhaust losses which are advantageous for DCEE since additional exhaust energy can be converted into useful work in the expander. In this work, the performance of isobaric combustion cycles in terms of indicated efficiency, emissions, and energy flow distribution is compared to the conventional diesel cycle but at a relatively lower compression ratio. A standard 17-compression ratio piston is replaced by a low 11.5-compression ratio piston. GT power simulations suggest that a low compression ratio of the high-pressure unit of DCEE could lead to an improvement in efficiency. The current study consists of two sets of experiments. In the first set of experiments, the intake pressure and intake temperatures are increased to match TDC temperatures and pressures of the previous study. The injected fuel amount is the same as in preceding work such that a direct comparison of energy flow is possible. In the second set of experiments, the fuel amount is increased to obtain the same air-fuel equivalence ratio. The experiments are conducted in a Volvo D13C500 single-cylinder heavy-duty engine.

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