Effect of Exhaust Blowdown Period on Pumping Losses in a Turbocharged Direct Injection Diesel Engine

In the paper some measurement results of pumping loops in a high-speed turbocharged D.I. Diesel engine have been presented with the aim to show how the exhaust blowdown period affects the pumping work. Cylinder pressure can drop deeply under the ambient pressure level during the blowdown period. Though this pressure is increasing during the main exhaust period still it remains below the subsequent intake pressure level. This phenomenon can be attributed to the so-called Kadenacy effect which was recognized and used for scavenging of a two-stroke engine as early as in the 1940's. This effect appeared to be strongly dependent on time of the blowdown period i.e. on the rotational speed.

In the paper relationships between thermal efficiency and pumping work have been presented. Furthermore, some measurements of cylinder pressure and calculation results of mass flow during the blowdown and exhaust periods have been analyzed. To the end with some conclusions about shape of the exhaust valve opening and possible gain of thermal efficiency while using the Kadenacy effect have been discussed.