Several studies in the literature treat the effects of ambient conditions and alternative fuel usage on the thermal and exergetic efficiencies of diesel engines. Different from other studies this study investigates the influence of the dwell time of multiple injection events on the thermal and exergetic efficiencies. A test engine was run using three different injection strategies. The main injection timing, the total fuel injected into the combustion chamber per cycle, the engine speed, the rail pressure and the intake manifold pressure were held constant, and the pre-injection timing was varied during the engine tests. Using the results of the engine experiments, the heat release rate, combustion temperature, heat balance, thermal efficiency, and exergetic efficiency were calculated. While it wasn't obtained any significant change in the thermal efficiency, exergetic efficiency and the exergy, the NOx emissions decreased by 7.4% via implementing appropriate pre-injection mass and injection advance. The combustion temperature and cooling heat loss decreased, while the exhaust heat loss increased when using the pre-injection strategies. The results demonstrate that pre-injection strategies, whose main goal is reducing NOx emissions, cause negligible losses in the thermal and exergetic efficiencies. (C) 2013 Elsevier Ltd. All rights reserved.