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In this work, in-cylinder pressure was measured in a 55 cc single cylinder, 4.4 kW, two stroke, spark ignition engine. In cylinder pressure measurements were taken using two different pressure transducers to determine if the performance differences between the two transducers are discernible in a small, spark ignition engine. A Kistler brand measuring spark plug was compared to a Kistler brand flush mount high temperature pressure sensor. Both sensors employ piezo-electric pressure sensing elements and were designed to measure indicated mean effective pressure as well as to detect knock at high temperature engine conditions. The pressure sensors were installed and adjusted to ensure cylinder volume after sensor installation matched the engine's original configuration within reasonable manufacturing tolerances. A series of tests at four throttle settings ensued to determine if either device altered the combustion volume or the engine's performance.

As IC engines decrease in displacement, their cylinder surface area to swept volume ratio increases. Examining power output of IC engines with respect to cylinder surface area to swept volume ratio shows that there is a change in power scaling trends at approximately 1.5 cm−1. At this size, it is suggested that heat transfer from the cylinder becomes the dominant thermal loss mechanism and performance and efficiency characteristics suffer. Furthermore, small IC engines (>1 cm−1) have limited technical performance data compared to IC engines in larger size classes. Therefore, it is critical to establish accurate performance figures for a family of geometrically similar engines in the size class of approximately 1.5 cm−1 in order to better understand the thermal losses that contribute to lower efficiencies in small IC engines. The engines considered in this scaling study were manufactured by 3W Modellmotoren, GmbH.

A two-port fuel-injection (PFI) system is added to a Rotax 914 four-cylinder spark-ignition engine to allow two fuels of different reactivity to be injected simultaneously in order to vary the fuel octane number during engine operation. Engine performance using the dual-fuel PFI system is compared to that using injection of primary-reference-fuel (PRF) blends via a single-PFI system for fuel octane ratings of 50, 70, and 87 octane. The on-the-fly octane control of dual-PFI system is found to control fuel-octane well enough to produce maximum indicated mean effective pressure (IMEPn) results within ± 2% of single-PFI PRF IMEPn results. IMEPn is compared among dual-PFI blends from 20 to 87 octane, neat n-heptane, neat JP-8, and JP-8/isooctane blends. Maximum IMEPn for these fuels is established for the Rotax 914 engine operating from 2500 to 5800 rev/min.