In the conventional approval test method of fuel consumption for heavy-duty diesel vehicles currently in use in Japan, the fuel consumption under the transient test cycle is calculated by integrating the instantaneous fuel consumption rate referred from a look-up table of fuel consumptions measured under the steady state conditions of the engine. Therefore, the transient engine performance is not considered in this conventional method. In this study, a highly accurate test method for fuel consumption in which the map-based fuel consumption rate is corrected using the transient characteristics of individual engines was developed. The method and its applicability for a heavy-duty diesel engine that complied with the Japanese 2009 emission regulation were validated.
The proposed test method comprises four processes: (i) obtaining experimental data for deriving the formula of transient correction factor (TCF); (ii) performing simulation for obtaining calculated data for deriving TCF formula; (iii) deriving this formula; and (iv) performing simulation of the fuel consumption by correcting the instantaneous fuel consumption by using TCF formula in addition to the conventional simulation method. In process (iii), the TCF formula is derived by multiple regression analysis with instantaneous data of the following explanatory variables: measured engine speed and its rate of change, measured torque and its rate of change. The ratio of measured instantaneous fuel consumption and estimated instantaneous fuel consumption based on the look-up table were considered as the objective variables.
The evaluation results of fuel consumption after the correction for the transient characteristics of the test engine showed that the calculation results with the correction were strongly correlated with experimental results. Thus, the proposed correction method for calculated fuel consumption effectively considered the transient characteristics of the engine. In addition, the engine speed and its rate of change and torque and its rate of change were established to be important parameters for deriving the TCF formula.
