This paper evaluates the lag time in a turbocharged single cylinder engine in order to determine its viability in transient applications. The overall goal of this research is to increase the power output, reduce the fuel economy, and improve emissions of single cylinder engines through turbocharging. Due to the timing mismatch between the exhaust stroke, when the turbocharger is powered, and the intake stroke, when the engine intakes air, turbocharging is not conventionally used in commercial single cylinder engines. Our previous work has shown that it is possible to turbocharge a four stroke, single cylinder, internal combustion engine using an air capacitor, a large volume intake manifold in between the turbocharger compressor and engine intake. The air capacitor stores compressed air from the turbocharger during the exhaust stroke and delivers it during the intake stroke. This work builds on previous theoretical and experimental work that shows that a turbocharger could be fitted to a single cylinder engine using an air capacitor to increase intake air density by 43% and peak power output by 29%.
Our previous research has shown that the capacitor works in steady state applications where turbocharger lag time does not matter. However, given the transient time to pressurize the capacitor, it will increase the already existing turbocharger lag time. The goal of this work is to show a clear correlation between capacitor size and transient response characteristics. By characterizing the transient response it will be possible to size an air capacitor for transient applications. An experimental setup was constructed to evaluate the time required to respond to an increased load on the engine at a constant speed, and the time it takes to increase engine speed at a constant load. We found that turbocharging had minimal effect on no load transient speed response. However, once load was applied to the engine, turbocharging increased the transient speed response time by a half of a second compared to a naturally aspirated engine. We also found that turbocharging affected the characteristics of the engine’s response to a change in torque at a constant speed. Larger Capacitors resulted in quicker initial response to a torque impulse then smaller capacitors but had approximately the same overall response time due to slower response as torque increased.