Exhaust Composition in a Small Internal Combustion Engine Using FTIR Spectroscopy


Kevin P. Horn

Date of Award


Document Type


Degree Name

Master of Science


Department of Aeronautics and Astronautics

First Advisor

Marc D. Polanka, PhD.


The mission-specific needs of small, remotely piloted aircraft demand lighter, more efficient engines with increased performance for their propulsion systems. A wide range of experimental efforts were undertaken to further the ability to obtain performance data on small engines as well as to develop understanding of their operation. Data were collected to quantify friction losses present in the dynamometer drivetrain on the small engine research bench. A correction and calibration model was developed for brake power collected by the dynamometer. Mechanical efficiencies for 28 cm3, 55 cm3 and 85 cm3 engines were 92.4%, 91.3% and 89.7%, respectively. Maximum fuel conversion efficiency for the three engines was calculated to be 14.9%, 15.4% and 18.3% at peak power, respectively. A 55 cm3 two-stroke engine was converted to electronic fuel injection and its performance was tested and compared to the same engine equipped with a carburetor. Peak power was comparable between carbureted and EFI configurations. Fuel consumption, as measured by brake specific fuel consumption, was reduced significantly. Time-averaged and crank-angle resolved methods for the analysis of exhaust gasses in a 55 cm3 two-stroke engine using Fourier transform infrared spectroscopy (FTIR) were developed and tested. Spectral features for CO2 and unburnt hydrocarbons (UHC) were resolved. The time-averaged absorbance measurements showed that short-circuiting, as a function of the concentration of UHC, followed delivery ratio (A) at wide open throttle.

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