Browse Publications Technical Papers 2019-01-0085
2019-01-15

Isobaric Combustion: A Potential Path to High Efficiency, in Combination with the Double Compression Expansion Engine (DCEE) Concept 2019-01-0085

The internal combustion engine efficiency is highly dependent on the peak pressure the engine operates at. The new compound engine concept, the Double Compression Expansion Engine (DCEE), utilizes a two-stage compression and expansion cycle to reach ultra-high efficiencies. This engine is expected to take advantage of its high-integrity structure adapted to high pressures, reaching 300 bar peak motored pressure. However, this will make conventional combustion cycles, such as the Seiliger-Sabathe (mixed) or Otto (isochoric) cycles, not feasible as they involve a further pressure rise due to combustion. This paper investigates the concept of isobaric combustion at relatively high peak-motored pressures and compares this concept with more traditional combustion modes in terms of efficiency and emissions. Multiple consecutive injections through a single injector are used for controlling the heat release rate profile to achieve different extent of isobaric heat addition, starting from near-isochoric and reaching near-isobaric conditions. In this study, the intake pressure is varied to enable a comparison between the isobaric cases with different peak pressures, up to 150 bar, and the mixed and near-isochoric cases. Tests are performed first, without EGR, and then with an optimized EGR level. Intake temperature is varied according to the DCEE boundary conditions. The experiments are performed on a 12.8L displacement 6 cylinder Volvo D13C500 engine utilizing a single cylinder with a standard 17-compression-ratio piston. The fuel used in all the experiments is a standard EU Diesel. In each target condition, the different injection strategies are compared with a total amount of fuel kept constant. The results offer more insight into the isobaric combustion concept and suggest the most favorable conditions and injection strategies for best efficiency without compromising on emissions, in the context of the high-pressure DCEE concept.

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