This article presents a means for turbocharging single-cylinder engines by buffering intake air between the exhaust and intake strokes using an air capacitor: an additional volume added in series to the intake manifold (Figure 1).
In addition to describing our approach, we analyze the feasibility of adding an air capacitor and a turbocharger to a single-cylinder engine using both theoretical modeling and experimental validation.
In this section, the theoretical feasibility of the air capacitor is analyzed, focusing on fill time, optimal volume, density gain that can be achieved by the system, and thermal effects due to adiabatic compression of the intake air.
The size of an air capacitor is a critical consideration for modeling turbocharger performance.
Equation 1 describes adiabatic expansion of air when treated as an ideal gas in the air capacitor.
Figure 2 demonstrates that the gain from increasing the volume of the air capacitor diminishes beyond 5 to 6 times the engine volume.
In this section, we describe the theoretical model constructed to characterize air flow from (1) the turbocharger to the capacitor, and (2) the air capacitor to the engine.
* The air capacitor was treated as a varying pressure source.
The theoretical model was constructed to characterize the pressure in the air capacitor as a function of turbocharger pressure.
The ideal gas law can then be used to calculate the mass flow into the air capacitor .
Figure 4 illustrates the transient response of the air capacitor using the IIM.
In the air capacitor, adiabatic compression by the turbocharger results in a pressure gain proportionally larger than the density gain in the intake air.