A new method for measuring fuel-injection rate

The paper deals with the basic principles of use and testing of the new met hod for measuring injected volumes of liquids. The above method was employe d in measuring the injected fuel volume in diesel injection systems, where fuel is injected at time intervals of up to 4 ms. It works by measuring the electric charge deposited by liquid droplets impacting a metal electrode. The electric charge is generated mainly in the injection nozzle, where the fuel rubs against the metal parts of injection nozzle, resulting in one por tion of free electrons moving from the metal to the fuel. The fuel then tra nsfers this electric charge to the sensor electrode. Rubbing merely serves to bring many points of the surface into good contact. The electric current appears also due to the temperature gradient in the sensor electrode. The temperature gradient in the electrode is a result of the transformation int o heat of kinetic energy of fuel droplets hitting the electrode at velociti es of 100-300 m s(-1). The electric charge is led from the electrode to the charge amplifier, where it is converted into electric current. The test re sults showed a very reliable operation of the sensor and a linear dependenc e of the area under the injection rate curve upon the injected fuel volume. The comparison of the injected rates measured with the charge and Bosch me asuring method, which is most frequently utilised today, showed a good matc hing of results in any operating regime. (C) 1999 Elsevier Science Ltd. All rights reserved.