Comparison between turbocharging and comprex pressure exchanger supercharging of high output diesel engines.

  • Colin A. Aldis

Student thesis: Doctoral ThesisPhD


The results contained within this thesis were taken from a largely experimental project tto compare a conventional turbocharger and the unique Comprex pressure wave supercharger. A large truck Diesel engine, the Leyland 690 was fitted in turn with a Holset H2B turbocharger and a Brown Boveri CX140 supercharger. A series of both steady state and transient investigations was completed with both systems. The turbocharged experimental results were also compared with predicted results from the steady state computer program (EMAT). The introduction gives; a detailed description of the Comprex operation, history, range and applications. The second chapter is devoted to a description of the apparatus and calibration of the instrumentation. The following four chapters give the experimental results in tabular and graphical form, for both systems and for the steady state and transient tests. In Chapter 7 the steady state tests for both systems are compared and the transient tests are compared in Chapter 8. The Comprex supercharger theory is briefly described in Chapter 9 with several ideas of the obtaining the air flow which bypassed the engine under certain conditions. The predicted results for the turbocharged engine are compared with experimental results in Chapter 10. Some of the problems encountered during the experimental testing are discussed in Chapter 11. With the engine operating under steady state conditions, the limiting torque curves for each system were slightly different. At the lower engine speeds (1400 - 8800 revs/min) the engine fitted with the Comprex produced a higher power than with the turbocharger. The specific fuel consumption at higher speeds was marginally better (lower) with the turbocharger but at lower speeds the Comprex produced favourable values. As expected, the boost pressure was higher with the Comprex wnth better air/fuel ratios particularly at the lower engine speeds. Using the Hart ridge smoke meter, the smoke levels with the Comprex were considerably better at the important lower engine speeds. Under transient conditions the Comprex produced considerably better results, especially in the response time to reach steady conditions. This was due to the higher boost pressure ratios at comparable operating conditions. During the very severe changes in load applied to the engine, the Comprex enabled stabilisation within 0.6 seconds compared with 1.5 seconds with the turbocharger. Transient smoke levels, measured by a high response opacimeter were also lower with the Comprex. Despite these very favourable results with the Comprex supercharger, its higher cost and weight, and the added complications associated with the drive and pipework, have so far militated against the wider adoption. However, for certain applications, such as tractors, excavators and shovel loaders with their rapidly changing load and speed cycles, the Comprex has considerable advantages.
Date of Award1982
Original languageEnglish
Awarding Institution
  • University of Bath

Cite this