The Effect of Crankshaft Phasing and Port Timing Asymmetry on Opposed-Piston Engine Thermal Efficiency

Alex G. Young, Aaron W. Costall, Daniel Coren and James W. G. Turner
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Alex G. Young: Institute for Advanced Automotive Propulsion Systems (IAAPS), University of Bath, Claverton Down, Bath BA2 7AY, UK
Aaron W. Costall: Institute for Advanced Automotive Propulsion Systems (IAAPS), University of Bath, Claverton Down, Bath BA2 7AY, UK
Daniel Coren: Institute for Advanced Automotive Propulsion Systems (IAAPS), University of Bath, Claverton Down, Bath BA2 7AY, UK
James W. G. Turner: Clean Combustion Research Center (CCRC), King Abdullah University of Science and Technology (KAUST), Jeddah 23955-6900, Saudi Arabia

Energies, 2021, vol. 14, issue 20, 1-20

Abstract: Opposed-piston, two-stroke engines reveal degrees of freedom that make them excellent candidates for next generation, highly efficient internal combustion engines for hybrid electric vehicles and power systems. This article reports simulation results that explore the influence of key control and geometrical parameters, specifically crankshaft phasing and intake and exhaust port height-to-stroke ratios, in obtaining best thermal efficiency. A model of a 0.75 L, single-cylinder opposed-piston two-stroke engine is exercised to predict fuel consumption as engine speed, load, crankshaft phasing, intake and exhaust port height-to-stroke ratios, and stoichiometry are varied for medium-duty truck and range extender applications. Under stoichiometric operation, optimal crankshaft phasing is seen at 0–5°, lower than reported in the literature. If stoichiometric operation is not mandated, best fuel consumption is achieved at an air-to-fuel equivalence ratio λ = 1.25 and 5–10° crankshaft phase angle, enabling a ~10 g/kWh (~4%) improvement in average brake-specific fuel consumption across medium-duty truck operating points. In range extender form, the engine provides 30 kW output power in accordance with a survey of range extender engines. In this role, there is a clear distinction between low-speed, high-load operation and vice versa. The decision as to which is more appropriate would be based on minimizing total owning and operating cost, itself a trade-off between better thermal efficiency (and thus lower fuel cost) and greater durability.

Keywords: opposed-piston two-stroke engines; crankshaft phasing; port height-to-stroke ratio; medium-duty truck; range extender; low carbon vehicles (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2021
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