Down-speeding diesel engines with two-stage turbochargers: Analysis and control considerations

Daryoush Mirza-Hekmati,Judith M Apsley,William P Heath,James R Forbes

doi:10.1177/1468087420976482

Daryoush Mirza-Hekmati, Judith M Apsley + Show 2 more

Open Access

https://doi.org/10.1177/1468087420976482

Copy DOI

Abstract

Diesel engines continue to be used in truck applications, so reducing fuel use and hence CO2emissions, is a priority. Single-stage turbocharged diesel engines are known to be fuel efficient under steady load at low speeds. However, the engine’s ability to track load transients becomes limited by emission constraints due to the rate of production values for smoke and the resulting higher nitrogen oxides (NOx). Modern air-path solutions including a variable geometry turbine (VGT) and high pressure exhaust gas recirculation (EGR) can be used to improve dynamic response without increasing NOxemissions, but lead to complex interactions that can be difficult to control. This paper develops a two-stage, in-series, air-path configuration, which improves the typical part-load performance at low engine-speeds through adjustments to the turbine expansion ratios. Better EGR rates (for NOxreduction) at low engine speeds can be achieved whilst the engine transient response is maintained. The air-path system is simulated using Ricardo Wave software and analysed for steady-state and transient behaviour in order to identify the relationships, constraints and performance measures for different operating regions that specify the controller requirements.

Highlights

The diesel engine is a mature technology for vehicle propulsion
In the engine simulation with two-stage in-series turbocharged air-path, the variable geometry turbine (VGT) rack position that sets the HPT flow area is set to 50% for 800 rpm – to supply sufficient intake air flow that is much needed at this engine speed
HPC in the absence of exhaust gas recirculation (EGR) disturbance effect: (a) pressure ratio and (b) speed, response with and without VGT adjustments, at engine speed of 800 rpm and 50 kW load followed by 50 kW step

Summary

Introduction

The diesel engine is a mature technology for vehicle propulsion. With the focus on carbon reduction, there is a move away from fossil-fuel engines to electric vehicles (EV). To exhibit the impact of lowering the operating speed on the engine’s efficiency and emission parameters, the engine with standard single-stage turbocharged air-path in Figure 1(a) is operated at three selected steady speeds of 800, 1300 and 1800 rpm under 50 kW of steady load.

Results

Conclusion