Numerical Simulation of the Injection Process in a Two Stroke Diesel Engine

In Diesel engines equipped with jerk injection pumps there appear many effects derived from fuel compressibility and the short duration of injection. As a result of them, cavitation, secondary injection, dribble and other hazardous phenomena may occur. With the objective of studying these processes, a simulation model for an indirect Diesel injection system has been developed. The mathematical model takes into account cavitation and gas dissolved effects. A relationship is obtained theoretically to reproduce the dependence of density of fuel oil with the pressure. The deduction of this equation is based on some hypotheses: that the amount of air in the liquid is constant, the process isothermal, the liquid fuel and its vapour are in thermodynamic equilibrium, and finally, that the temperature, pressure and velocity of both phases are identical. The unidimensional two-phase flow equations are simplified and employed to resolve the high-pressure line. The numerical solution is obtained with an explicit difference method that follows the physical direction of propagation of information into the line. and theoretical results are compared with experiments. The test bench has been prepared to record signal of pressure in two points of the high-pressure line and needle lift is measured. Tests have been carried out with a Bosch PFE1Q55 injection pump and a pintle nozzle. The numerical and experimental results show good agreement, tracking secondary injections even when cavitation is present in the system.