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This analysis was undertaken to improve the understanding of the throttle and fuel types, exhaust gas recirculation, and mileage that affect the thickness and location of throttle deposit formation. Some automotive internal combustion engine throttle bodies have experienced field issues causing increased torque in the opening direction or idle stability/stalls. To increase the understanding of the factors affecting throttle deposit formation, a measurement system was developed to quantify throttle deposit thickness. Furthermore, an analysis of variance was completed on throttles from known field usage to identify factors such as oil type, fuel type, EGR, throttle type that affect deposit thickness. Through an analysis of field vehicles with known history and throttle deposits this initial analysis identifies the key factors affecting throttle deposit build up.

The performance and exhaust emissions of a commercially available, propane fueled, air cooled engine with Electronic Fuel Injection (EFI) were investigated by varying relative Air to Fuel Ratio (λ), ignition timing, and Compression Ratio (CR). Varying λ and ignition timing was accomplished by modifying the EFI system using TechniCAL Industries’ engine development software. The CR was varied through using pistons with different bowl sizes. Strong relationships were recorded between λ and ignition timing and the resulting effect these parameters have on engine performance and emissions. Lean operation (λ > 1) has the potential to significantly reduce NOx production (110 g/kW-hr down to 5 g/kW-hr). Unfortunately, it also reduces engine torque by up to an order of magnitude (31 Nm down to 3 Nm).

Natural gas is a viable alternative to gasoline and diesel fuel because it is a clean burning fuel that is available from a large domestic reserve through a mature infrastructure. The heavy dependence of the small engine sector on oil, much of which is imported from foreign countries and the small engine sector's negative impact on the air quality in urban areas are two pervasive problems that can be helped by using Compressed Natural Gas (CNG) as a small engine fuel. In addition, CNG is typically over 80% methane, which is produced by the decay of organic material, so while natural gas is not renewable its use enables much of the infrastructure required for a methane-based renewable energy system. In order to determine the emissions benefit of using CNG as compared to gasoline in a small engine, a 750 cc 90 degree V Twin port-fuel-injected production engine rated at 29 horsepower (HP), designed and built by Kohler Inc.