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For a fuel system with a tangent cam or a constant-velocity cam, the peak injection pressure continues to rise as the injection duration increases, but overly high peak pressures induce mechanical loads and wear, limiting the maximum engine speed and injection quantity. To improve the performance of an EUP (Electronic Unit Pump) fuel system for heavy-duty diesel engines, this work proposes a new pump cam, namely the constant-pressure cam. It helps the EUP run at a higher speed and deliver larger fuel quantities while maintaining a constant peak injection pressure, which improves the power of the heavy-duty diesel engine. A model based on the EUP was built to determine the three constraints for optimising the constant-pressure cam: 1) the pump pressure should equal the nozzle pressure; 2) the cam speed should decrease with the increase in the injection duration; and 3) the cam acceleration gradient should be zero. An EUP system was tested with the tangent cam and the optimised cam under different conditions. The experimental results show that the EUP system with the optimised cam delivers more injection quantity and runs at higher engine speeds while maintaining the same peak pressure as the tangent cam.

The fuel injectors in a heavy-duty diesel engine with a selective catalytic reduction (SCR) system operate in harsh conditions that cause them to deteriorate, resulting in changes in the fuel injection quantity. In this study, a method for determining the injection quantity of fuel injected using the output of a NOx sensor in a heavy-duty diesel engine equipped with a SCR system is developed. A mathematical model was derived to calculate the fuel injection quantity based on the oxygen concentration in the exhaust gases. Bench tests were conducted at various engine operating conditions. The results indicate that at high engine loads, the absolute error between the oxygen concentration measured by the NOx sensor and that measured by a gas analyser was less than 2%, which is acceptable, and the reactions in the SCR reactor consumed no more than 1% of the oxygen in the exhaust gases, which is negligible. An analysis of the model demonstrates that the calculated value of the injection quantity based on the oxygen concentration in the exhaust is more accurate for lower oxygen concentrations (i.e., at greater engine loads). The test data reveal that the error in the fuel injection quantity obtained from the model was less than 2% at high engine loads. This research demonstrates that the on-board calculation of the fuel injection quantity based on the oxygen concentration signals from the NOx sensor is possible at high engine loads.

Because of the stringent nitrogen oxides (NOx) emissions legislation for heavy-duty diesel engines, the SCR (selective catalytic reduction) has been investigated by many researchers. The objective of these studies is to investigate the reasons why the temperature downstream of the SCR catalyst is not always equal to that upstream with a commercial V2O5 catalyst applied in a heavy-duty diesel engine. Using the energy conservation equation and SCR reaction model, a method for estimating the exhaust gas temperature downstream of the catalyst was proposed. The SCR downstream temperature was calculated and experimentally measured under the standard ESC (European steady-state cycle) and different speeds and torques. The results indicated that when the diesel engine operated under steady-state conditions, the temperature downstream of the catalyst was similar to that upstream. Compared with the change of the temperature upstream of the catalyst, the change of downstream is delayed under unsteady-state conditions. According to the analysis, the main reason for this result is that temperature gradients exist along the substrate channels, accounting for inter-phase (gas–solid) heat transfer. The downstream temperature estimation is important for confirming the SCR catalyst temperature.

This work investigated the impacts of biodiesel properties on the complete fuel injection process of a high-pressure unit pump (UP) fuel system. Analysis based on a one-dimension flow model in the UP system deduces that both the injection pressure and the pressure changing rate may be affected by the fuel properties. A serial of experiments were conducted under varied operation conditions to compare the influences of the diverse fuel properties on the fuel injection process. The test results verify this deduction that the different properties of biodiesel have considerable influences on the process of pressure building. The peak injection pressure of biodiesel fuel is relatively higher than that of diesel. In addition, for biodiesel, the changing rate of the rising process of the injection pressure is also faster. However, the fuel properties have no obvious effects on pressure drop process. Meanwhile, the injection timing advance becomes larger as biodiesel fuel is used. Furthermore, with the increase of fuel pressure, the influences of fuel properties on injection increase.