 The engine has been in production since 2001, with over 10 million units sold as of April 2013.Improvements over this period have included coating the tappets to reduce friction by 40%; redesigning the injector spray angle, resulting in a 15% reduction of during combustion and a small improvement in torque; and fitting new piston rings, reducing the tension on the belt-driving engine accessories and optimizing the dimensions of the base engine.The injection pattern has been altered to have two pilot injections over a wide operating range, reducing combustion noise by up to 3 decibels.