Advanced fuel injection systems have been classified as key to the future of diesel in both light-duty and heavy-duty vehicles. These systems will be instrumental in developing new engines that will comply with future emissions regulations. Modern fuel injection systems are one of the main reasons the diesel vehicle market has grown so rapidly in Europe with two predominant types: high-pressure, electronically-controlled unit injectors and the common rail system. Although this technology first appeared in heavy-duty trucks and buses, there is great potential for these diesel fuel injection systems for passenger vehicles.