Analytical modeling of fuel consumption and regulated exhaust emission rates for trucks

Abstract

Climate change due to greenhouse gas emissions led to new vehicle emissions standards which in turn led to a call for vehicle technologies to meet these standards. Modeling of vehicle fuel consumption and emissions emerged as an effective tool to help developing and assessing such technologies. Although vehicle analytical models are favourable in many cases due to describing the physical phenomena associated with vehicle operation based on the principles of physics and with explainable mathematical trends and with extendable modeling to other vehicle types, no analytical model has been developed and experimentally validated as yet of diesel fuel consumption and exhaust emissions rate. The present study analytically models diesel fuel consumption rate microscopically for the accelerating, cruising and decelerating modes of driving a vehicle and models diesel regulated emissions rate for the cruising mode of driving a vehicle. In order to make these models, an analytical model of the following subsystems has been made: (i) intake manifold taking the flexibility of crankshaft and air density into account, (ii) supercharging diesel centrifugal compressor, (iii) multi-cylinder supercharged diesel engine, (iv) diesel fuel system and engine power, (vi) exhaust system and the percentage of unburned fuel. Sensitivity analysis has been conducted for simplifying the models in order to fit the INTEGRATION software and traffic simulator. The models have been validated experimentally against field data. For the rate of diesel fuel mass flow, the average percentage of deviation was 1.8% for all standard cycles outperforming widely recognized models such as the CMEM and VT-Micro. The simulated results have been analyzed statistically for the rate of diesel fuel mass flow with coefficient of determination and relative error of 96% and 1.2%, respectively. The average percentage of deviation of 7% 1.7%, 1.9%, 2%, and 10.6% for the diesel engine power, CO emission, NOx emission, HC emission, and percentage of unburned fuel respectively, for all Freeway cycles outperforming widely recognized models such as the CMEM and VT-Micro. The simulated results have been analyzed statistically as well with coefficient of determination of 73%, 99%, 99%, 83%, and 70% respectively. The corresponding relative error has been 7%, 3%, 1.7%, 2%, and 10.6% respectively. Moreover, the developed analytical models of the intake manifold gas speed dynamics, in-cylinder gas speed dynamics, supercharging compressor power, supercharging compressor mechanical efficiency, and supercharged air density have been experimentally validated using case studies with an average of deviation from field data of 12.6%, 11%, 3%, 8%, and 3.7%, respectively. The simulated results have been analyzed statistically as well with relative error of 12.6%, 11%, 3%, 8%, and 3.7%, respectively. In addition to devising two new classifications, which are the formulation approach-based modelling and main input variable-based modelling, the models developed in this study are (a) widely valid models which are not restricted to a specific dataset, (b) an effective tool to quickly judge whether the related experimental measurements make sense or not, (c) show which chemical reaction within the powertrain kinetically influences significantly emissions rate. Keywords: Vehicle Fuel Consumption; Vehicle Regulated Emissions; Modeling; Diesel Powertrain