Fuel injection system with fuel preheating and with a fuel-cooled pressure regulating valve

A fuel injection system for internal combustion engines, including a high-pressure fuel pump (7), a common rail (9), at least one injector receiving fuel from the high-pressure fuel pump (7) via the common rail (9), a prefeed pump (1) that pumps out of a tank (3) to the high-pressure fuel pump (7) via a supply line (5), a return line (33) for carrying fuel away from the common rail (9), a pressure regulating valve (13) disposed between the common rail (9) and the return line (33), a leakage line (23) for carrying fuel away from the high-pressure fuel pump (7), and control means (27) for selectively connecting the pressure regulating valve (13) with the supply line (5b) as a function of the temperature of the fuel in the supply line (5, 5a, 5b) whereby fuel from the prefeed pump (1) flows through the pressure regulating valve (13) prior to being supplied to the high-pressure fuel pump (7).