Efforts to improve the range and endurance of group 2 (10–25 kg), internal combustion engine (ICE) powered unmanned aerial vehicles (UAVs) have been underway for several years at Air Force Research Laboratory (AFRL). To obtain the desired performance improvements, research into improving the overall efficiency of the ICE powerplants is of great interest. The high specific energy of hydrocarbon fuels (13,000 W h/kg for gasoline), but low fuel conversion efficiency for small ICEs means that relatively minor improvements in the fuel conversion efficiency of the engines can yield large improvements in range and endurance. Little information is available however for the efficiency of ICEs in the size range of interest (10–200 cm3 displacement volume) for group 2 UAVs. Most of the currently available efficiency data for 10–200 cm3 ICEs is for two-stroke engines. The goal of this study was to provide an in-depth probe of the efficiency and energy losses of a small displacement four-stroke engine which could potentially be used to power a group 2 UAV. Energy balances were performed on a Honda GX120 four-stroke engine using empirical research methods. The engine was a 118 cm3 displacement, single cylinder ICE. Energy pathways were characterized as a percentage of the total chemical energy available in the fuel. Energy pathways were characterized into four categories: brake power, cooling load, exhaust sensible enthalpy and incomplete combustion. The effect of five operating parameters was examined in the study. Fuel conversion efficiency ranged from 22.2% to 25.8% as engine speed was swept from 2000 to 3600 RPM, from 20.8% to 27.3% as equivalence ratio was swept from 0.85 to 1.25, and from 15.7% to 24.9% as throttle was swept from 28.5% to 100%. Combustion phasing and cylinder head temperature sweeps showed only minor changes in fuel conversion efficiency.

References

References
1.
Finnegan
,
P.
,
2016
, “
Press Release: UAV Production Will Total $93 Billion
,” The Teal Group Corporation, Fairfax, VA, accessed May 20, 2016, http://www.tealgroup.com
2.
U.S. Air Force
,
2005
, “
The U.S. Air Force Remotely Piloted Aircraft and Unmanned Aerial Vehicle Strategic Vision
,” U.S. Air Force, Washington, DC.
3.
Ausserer
,
J.
,
Polanka
,
M.
,
Litke
,
P.
, and
Grinstead
,
K.
, 2017, “
The Scaling of Loss Mechanisms in 1–10 kW Two-Stroke Internal Combustion Engines
,”
SAE Int. J. Engines
,
10
(2), pp. 128–143.
4.
Menon
,
S.
, and
Cadou
,
C.
,
2013
, “
Scaling of Miniature Piston-Engine Performance Part 1: Overall Engine Performance
,”
J. Propul. Power
,
29
(
4
), pp.
774
787
.
5.
Ausserer
,
J.
,
2016
, “
Scaling of Heat Transfer and Loss Mechanisms in Small Scale Internal Combustion Engines
,” Ph.D. thesis, Air Force Institute of Technology, Wright-Patterson Air Force Base, OH.
6.
Baranski
,
J.
,
2013
, “
Experimental Investigation of Octane Requirement in a Turbocharged Spark-Ignition Engine
,” M.S. thesis, University of Dayton, Dayton, OH.
7.
3W-Modellmotoren
,
2016
, “
3W Engines and Airplanes
,” 3W-Modellmotoren GmbH, Hanau, Germany, accessed July 13, 2016, http://3w-modellmotoren.de
8.
American Honda Motor
,
2014
, “
Honda Gx Series Engines
,” Sales Brochure, Alpharetta, GA.
9.
Heywood
,
J.
,
1988
,
Internal Combustion Engine Fundamentals
,
McGraw-Hill
,
New York
.
10.
SAE
,
2011
, “
Instrumentation and Techniques for Exhaust Gas Emissions Measurement
,” SAE International, Warrendale, PA, SAE Standard No.
J254_201106
.http://standards.sae.org/j254_201106/
11.
Turns
,
S.
,
2012
,
An Introduction to Combustion: Concepts and Applications
,
McGraw-Hill
,
New York
.
12.
NIST
,
2016
, “
NIST Chemistry Webbook
,” National Institute of Standards and Technology, Gaithersburg, MD, accessed Oct. 21, 2014, http://webbook.nist.gov
13.
Ausserer
,
J.
,
Horn
,
K.
,
Polanka
,
M.
,
Litke
,
P.
, and
Grinstead
,
K.
,
2015
, “
Quantification of Short-Circuiting and Trapping Efficiency in a Small Internal Combustion Engine by GC-MS and GC-TCD
,”
SAE
Paper No. 2015-32-0716.http://papers.sae.org/2015-32-0716/
14.
Taylor
,
C.
,
1985
,
The Internal Combustion Engine in Theory and Practice: Volume 1: Thermodynamics, Fluid Flow, Performance
,
MIT Press
,
Cambridge, MA
.
You do not currently have access to this content.