The stringent emission regulations coupled with tighter CO2 targets demand extreme optimization of the diesel engines. In this context, it is important to minimize the cylinder bore distortions in cold and hot conditions. The cold bore distortion is primarily due to the assembly forces applied by the cylinder head bolts whereas the hot distortion is a resultant of local metal temperatures and structural rigidity. The present work describes the extreme optimization techniques used to reduce the bore distortion of a modern high power-density (60 kW / lit) diesel engine, Moreover, the benefits of reducing the bore distortion are quantified in terms of cylinder system friction, blowby rate, oil consumption (OC) and ash loading rate of the diesel particulate filter (DPF).
An optimized torque plate honing is used to reduce the bore distortion in cold conditions. However, an extreme optimization of the cylinder bore structure and water jacket design was needed to control the hot bore distortion. With the reduced bore distortion, the engine could be optimized to have a reduced tangential force. The cumulative tangential force of all the piston rings could be reduced from 37 N to 23.5 N which could result in a significant reduction in the cylinder system friction. Moreover, the engine level measurements with and without the torque plate honing confirm that a significant reduction in blowby rate (approximately 20 %) and oil consumption (approximately 25 %) could be achieved with the torque plate honing. The results were found to be consistent with the vehicle level results of the oil consumption (g/km).
Furthermore, the reduction in oil consumption could benefit the ash loading behaviour of the DPF. With the low bore distortion (LBD) engine, the ash loading rate of the DPF could be reduced significantly which is extremely important to have consistently higher regeneration intervals throughout the life of the vehicle. Thus, the development approach to have low bore distortion has resulted in multiple benefits and hence it is found to be useful in developing diesel engines with compliance to future regulations.