Why are NCI Pistons Not Used in Heavy Duty Diesel Engines?

In order to meet the strict exhaust emission legislation and customer's requirements of high power, heavy-duty diesel engines have to have a higher peak firing pressure and higher thermal load recently. It causes serious influence on the reliability and durability of the engines and engine parts, pistons in particular. The pistons for the next generation heavy-duty diesel engines are required to withstand more than 20 MPa of the peak firing pressure and higher thermal load, productivity of course. Nodular cast iron (NCI) pistons are one of the answers that could satisfy the requirements mentioned above. It is well known that NCI pistons have a lot of advantages but not popular. The difficulty of the casting technology and the quality control are the major reasons. Hino P11C engine has adopted it and kept it under mass production since 1991 and approx.20000 units of total production volume without any troubles. Newly developed gravity die casting technology could remove these problems and it could realize the high quality NCI piston castings. This paper describes the advantages of the NCI pistons comparing with the steel mono-block pistons and the articulated pistons and also describes the gravity die casting technology that eradicated those difficulties of the casting.