Changes in the tightness of the combustion chamber of an diesel engine during long-term operation

The paper presents results of research on changes in the tightness of the combustion chamber during long-term operation. The study was conducted on 5 six-cylinder diesel engines with a swept volume of 6.8 dm mounted in medium size trucks. All 5 trucks were used and serviced in similar conditions. The changes in the tightness o f the combustion chamber were determined on the basis of the results of periodical measurements of maximum compression pressure in cylinders, drop of pressure during a cylinder leakage test and blowby rate under different conditions of engine operation. The investigation was carried out in the range of vehicle mileage of 0-450,000 km. The results show ed that in the initial period of engine use (0-40,000 km) the tightness of the combustion chamber improved, after which it gradually deteriorated. For mileages of over 40,000 km, the significance of linear correlations between results of all tightness measurements and mileage were conflrmed and regression lines were determined. Mean rates of changes in the individual tightness parameters differed considerably among one another. Mazimum compression pressure changed the slowest and blowby the fastest together with mileage. Mean value of maximum compression pressure at 440,000 km was only 13% lower than at 40,000 km, whereas blowby rate at full engine loadat 2200 rpm was 125% higher.