On-Board Fuel Property Identification Method Based on Common Rail Pressure Signal

Abstract

This paper investigates the impact of fuel property variations on the rail pressure fluctuations in high pressure common rail (HPCR) systems and explores the possibility of indentifying fuel physical property based on the measurement of a rail pressure sensor. Fluid transients, particularly the water hammer effect, in a HPCR system are discussed and the 1D-governing equations are given. A HPCR model is developed in GT-Suite. The injectors, a three-plunger high pressure pump, and a pressure control valve are modeled in a relatively high level of detail. Five different fuels are modeled and their properties including density, bulk modulus, and acoustic wave speed are validated. Simulation results are obtained under different conditions with variable rail pressures and injection durations. The results show that natural frequency of the common rail varies with the fuel type filled in it. By applying the Fast Fourier Transform to the pressure signal, the differences of fuel properties can be revealed in the frequency domain. Since the rail pressure natural frequency is affected by the acoustic wave speed in the fuel, it can be concluded that this approach not only works for biodiesel blend level estimation, but also universally applies to the identification of various fuels and their blends as long as the acoustic wave speed in the fuel is known and the difference comparing to regular diesel is discernable.Copyright © 2012 by ASME