In a first series of tests in which the overall effects of intake charge throttling were demonstrated, only air was used as the inlet charge and cylinder number one was throttled isothermally from 10 g/s to 8.5 g/s in steps of 0.5 g/s. A second series of tests was then run by throttling the inlet charge over the same range of mass flow rate while maintaining the oxygen mass flow (and mass of oxygen trapped in the cylinder) constant. The specific heat capacity of the inlet charge for the second series of tests was also kept constant and equal to that of air. This was achieved by injecting into the inlet manifold calculated amounts of oxygen and helium, whilst throttling the inlet charge air.
Comparison of the results from the two series of tests enabled the following question to be answered: when the inlet charge mass is reduced, is the reduction in the charge mass itself that is important, or is the consequent reduction in the amount of oxygen mass trapped that controls the emissions?
It was found that the NOx emissions increased somewhat due to the reduction in total inlet charge mass. However, CO, UHC, and smoke emissions increased substantially due to the reduction in the amount of oxygen trapped.