The dynamic characteristics of a diesel fuel injection system have a remarkable affect on the cyclic fluctuation of engine speed which is called “hunting”. The simulation analysis on these characteristics are discussed in this paper.
First, we conducted experiments on frequency response of mechanical governors on the test stand. However, we could not establish good correlation between the experimental results and the calculations using the “linear governor equation” method. We investigated the results in detail, and by using a non-linear governor equation - “Itoh's equation”, we could simulate the dynamic characteristics of the governor quite well. However, after Itoh's equation was used in the “hunting” simulation, we still could not get good correlation between the experimental results and the calculation of “hunting”. Next, we have investigated the inditial response of fuel delivery characteristic. In these studies, the following was proven:
- (1)
The “overshoot” or “undershoot” phenomena of. fuel delivery exist in a limited zone, and this quantity and zone cannot be neglected for “hunting” analysis.
- (2)
This phenomenon is dependent on the change of residual pressure in the injection pipe.
Taking the results into consideration, we have created a simulation model of the dynamic characteristics of fuel delivery. “Injection Potential” (representing residual pressure in injection pipe) is introduced into this model. Using “Itoh's equation” and the fuel delivery model for “hunting” simulation, the accuracy of simulation (zone, frequency and quantity of “hunting” fluctuation) are remarkably improved.
Therefore, we believe the information in this paper offers a great help for development and improvement of fuel injection system.