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During the past years, extensive research efforts have led to the development of diesel engines with significantly improved power concentration and fuel efficiency as compared to the past. But unfortunately, the increase of engine thermal efficiency is accompanied by a sharp increase of peak cylinder pressure. At the moment, peak pressures in the range of 230-240 bar have been reported. Naturally, a question remains as to whether such increased peak pressures could have an overall detrimental impact on mechanical efficiency. Initially, it was expected that these would have a negative impact and this was the motive for conducting the present work and developing a detailed friction model. Up to now, various correlations have been proposed that provide the friction mean effective pressure as a function of engine speed and load mainly, neglecting the effect of peak pressure or using data up to 130-140 bar.

The direct injection heavy-duty diesel engine is the main propulsion unit for trucks, lories and other heavy-duty vehicles mainly due to its superior efficiency when compared to other existing reciprocating engines. However, this engine suffers from relatively high particulate and nitric oxide emission levels. Considering current legislation for emissions and especially future limits, it seems that a great deal of research is required to satisfy these limits and maintain efficiency at a high level. As widely recognized, the fuel injection mechanism plays an important role for both engine performance and pollutant emissions. The major problem is to seek solutions that enable the control of major pollutants, nitric oxide and particulate matter. For this reason, various injection rate shapes have been proposed which require sophisticated fuel injection equipment and extremely high fuel injection pressures. Now two main categories are considered, common rail fuel injection system and PLN.