This paper presents a feasibility study of a method for turbocharging single cylinder, four-stroke internal combustion engines. Turbocharging is not conventionally used with single cylinder engines because of the timing mismatch between when the turbo is powered, during the exhaust stroke, and when it can deliver air to the cylinder, during the intake stroke. The proposed solution involves an air capacitor on the intake side of the engine between the turbocharger and intake valves. The capacitor acts as a buffer and would be implemented as a new style of intake manifold with a larger volume than traditional systems.
In order for the air capacitor to be practical, it needs to be sized large enough to maintain the turbocharger pressure during the intake stroke, cause minimal turbo lag, and significantly increase the density of the intake air. By creating multiple flow models of air through the turbocharged engine system, we found that the optimal size air capacitor is between four and five times the engine capacity. For a capacitor sized for a one-liter engine, the lag time was found to be approximately two seconds, which would be acceptable for slowly accelerating applications such as tractors, or steady state applications such as generators. The density increase that can be achieved in the capacitor, compared to air at standard ambient temperature and pressure, was found to vary between fifty percent for adiabatic compression and no heat transfer from the capacitor, to eighty percent for perfect heat transfer. These increases in density are proportional to, to first order, the anticipated power increases that could be realized with a turbocharger and air capacitor system applied to a single cylinder, four-stroke engine.