Engine-Control Impact on Energy Balances for Two-Stroke Engines for 10-25 kg Remotely-Piloted Aircraft

[+] Author and Article Information
Joseph K. Ausserer

USAF Test Pilot School 220 Wolfe Ave Edwards AFB, CA 93524

Marc D. Polanka

Air Force Institute of Technology 1950 Hobson Way WPAFB, OH 45433

Paul J. Litke

Air Force Research Laboratory 1950 7th St WPAFB, OH 45433

Jacob A. Baranski

Innovative Scientific Solutions Inc. 1950 7th St WPAFB, OH 45433

1Corresponding author.

ASME doi:10.1115/1.4039466 History: Received January 01, 2018; Revised January 22, 2018


The rapid expansion of the market for remotely-piloted aircraft (RPA) includes a particular interest in 10-25 kg vehicles for monitoring, surveillance, and reconnaissance. Power-plant options for these aircraft are often 10-100 cm3 internal combustion engines (ICEs). The present study builds on a previous study of loss pathways for small, two-stroke engines by quantifying the trade space among energy pathways, combustion stability, and engine controls. The engine controls considered in the present study are speed, equivalence ratio, combustion phasing (ignition timing), cooling-air flow rate, and throttle. Several options are identified for improving COTS-engine efficiency and performance for small, remotely-piloted aircraft. Shifting from rich equivalence ratios to lean operation results in a 4% (absolute) increase in fuel-conversion efficiency at the expense of a 10% decrease in power. The stock, linear timing maps are excessively retarded below 3000 rpm, and replacing them with custom spark timing improves ease of engine start. Finally, in comparison with conventional-size engines, the fuel-conversion efficiency of the small, two-stroke ICEs improves at throttled conditions by as much as 4-6% (absolute) due primarily to decreased short-circuiting. A case study shows that at 6000 rpm, the 3W 55i engine at partial throttle will yield an overall weight saving compared to the 3W 28i engine at wide-open throttle for missions exceeding 2.5 hr (at a savings of ~5 g/min).

Section 4: U. S. Gov Employees
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