A study on the effects of engine size on diesel engine efficiency and combustion characteristics

[+] Author and Article Information
Jue Li

Texas A&M University. USA, 3123 TAMU, College Station, TX, USA

Timothy J. Jacobs

Texas A&M University. USA

Tushar Bera

Shell Global Solutions (US), Inc.

Michael Parkes

Shell Research Limited, UK

1Corresponding author.

ASME doi:10.1115/1.4040092 History: Received June 20, 2017; Revised February 20, 2018


This study investigates the effects of engine bore size on performance characteristics including: in-cylinder pressure, ignition delay, burn duration, and fuel conversion efficiency, using experiments between two engines of different bore sizes. The two engines are nearly identical, except bore size, stroke length, and consequently displacement. Although most of this diagnosis is done with experimental results, a 1-D model is also used to calculate turbulence intensities with respect to geometric factors; these results help to explain observed differences in heat transfer characteristics. The results are compared at the same brake mean effective pressure, and show that engine bore size has a significant impact on the indicated efficiency. The larger bore engine has a higher indicated efficiency. Although the larger engine has higher turbulence intensities and longer burn duration, the lower surface area to volume ratio and lower reaction temperature leads to lower heat losses to the cylinder walls. The difference in the heat loss to the cylinder walls between the two engines is found to increase with increasing load. In addition, due to the smaller volume-normalized friction loss, the larger sized engine also has higher mechanical efficiency. In the net, since the brake efficiency is a function of indicated efficiency and mechanical efficiency, the larger sized engine has higher brake efficiency with the difference in brake efficiency between the two engines increasing with increasing engine load. In the interest of efficiency, larger bore designs for a given displacement could be a means for future efficiency gains

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