A study on emissions improvement of a diesel engine equipped with a mechanical supercharger

Abstract

The engine performance and emissions from a 3 l diesel engine equipped with a mechanical supercharger are investigated experimentally, and the advantages and disadvantages of the mechanical supercharger system are discussed in a comparison with performances and emissions from a corresponding 3 l diesel engine equipped with a turbocharger. An experiment conducted under steady-state conditions shows that the mechanical supercharger delivers higher boost pressures than the turbocharger under steady-state low- and middle-load operating conditions, and that the higher boost pressure allows the application of higher amounts of exhaust gas recirculation (EGR), which leads to lower NOx emissions. In a transient test, the fuel flowrate is increased instantly from a low to high rate at a constant engine speed, and T₉₀, which is the time required for the mechanical supercharger to achieve 90 per cent of the steady-state boost pressure, is found to be considerably shortened as compared to T₉₀ obtained in a similar test with a corresponding turbocharged engine. In addition, the Japanese JE05 test result shows that NOx emission from the 3 l engine equipped with the mechanical supercharger is lower by 50 per cent than the engine with the turbocharger at a common level of soot emissions. However, the fuel consumption rate is worsened by 5.5 per cent due to the drive loses of the supercharger. Further study for reducing the fuel penalty is necessary to apply the mechanical supercharger to practical diesel engine systems.