Mathematic Model And Effect Study For Commercial Vehicles Fuel Economy And Waste Heat Recovery

With the serious energy situation and enhancement of the emission regulation, the requirement for the automobile fuel economy increased. Lack of mathematic model and analysis method of commercial vehicle fuel economy and relevant fuel consumption data would cause a difficulty when design a commercial vehicle, especially for configuring the powertrain under the customers' request. So, research on the commercial vehicle fuel economy could calculate and predict the commercial vehicle fuel consumption effectively, provide technical guidance for vehicle design and reference and basis for China making commercial vehicle fuel consumption limit laws and regulations. Compared to a passenger vehicle, the commercial vehicle has a larger displacement engine and running a longer time, its waste heat recovery could improve engine thermal efficiency, reduce the fuel consumption and emissions, better the fuel efficiency, realize the energy regeneration.This dissertation focused on the commercial vehicle, based on theoretical derivation, simulation analysis and engineering test, setup and verified the commercial vehicle fuel economy mathematic model and waste heat recovery mathematic model, proposed a simulation analysis method by using computer simulation and test, analyzed the impact factor both of commercial vehicle fuel economy and waste heat recovery as well as the waste heat recovery how to affect the commercial vehicle fuel economy. The main research contents were as follows:1. For the purpose of commercial vehicles fuel economy, based on fuel economy evaluation index and related entities, proposed a simulation method and analysis process for fuel economy; based on engine theory and vehicle dynamics, setup a mathematic model for the engine impetus, combustion and economic performance index and vehicle steady and transient states, determined the relationship between engine and vehicle dynamics then concluded the commercial vehicle fuel economy mathematic model and its impact factors.2. After comparing to the currently research methods of vehicles fuel economy, proposed a novel method for calculating the commercial vehicles fuel economy based on vehicle speed tracking. By taking the advantage of MATLAB/Simulink, setup simulation models for driver intention and shifting logic, engine and transmission, vehicle dynamics and conclude the commercial vehicle fuel economy simulation analysis model; in order to validate the simulation analysis model, a road test was conducted by the researcher and data results logged to compare with the simulation model results, then the simulation results was testified effectiveness, finally form an approach combining with computer simulation and road test.3. According to the commercial vehicle fuel economy mathematic model and simulation model, using the simulation analysis method, analyzed the fuel economy at different driving cycles, transmission system gear ratio and shifting logic, the influence of different driving cycles and shifting logic to fuel economy and optimized methods of transmission gear ratio were proposed, provided an application case for commercial vehicle fuel economy.4. Based on thermodynamics, heat and mass transfer and fluid mechanics knowledge, Rankine cycle as a basis of waste heat recovery cycle was adopted and the effectiveness-NTU method was used to setup the waste heat recovery mathematic model, proposed a calculation method for boiler performance based on engine operation conditions and deduced the relationship between Rankine cycle working fluid mass flow rate and engine exhaust mass flow rate;the waste heat recovery test bench was setup, the waste heat recovery parameters was collected by running a baseline engine condition, through the baseline results, the simulation parameters were calculated by waste heat recovery mathematic model, and verified the waste heat recovery mathematic model by comparing the baseline test and simulation results.5. Based on calculation formula of engine exhaust mass flow rate, analyzed the waste heat recovery boiler outlet temperature, turbine outlet temperature, output net power, thermal efficiency, boiler heat capacity ratio, boiler effectiveness and engine brake thermal efficiency, obtained the relationship between the working fluid mass flow rate and engine exhaust mass flow rate, proposed a select method for working fluid mass flow rate when reaching the waste heat recovery max net output power and thermal efficiency; based on the engine different operation conditions, the performance chart of commercial vehicle engine speed-throttle position-waste heat recovery net output power was achieved to provide the reference for commercial vehicle waste heat recovery electronic control unit; a correlation model with fuel economy and waste heat recovery model was setup, based on a driving cycle, the fuel consumption data was achieved and grounded the waste heat recovery apply to commercial vehicles.The dissertation results would lay a foundation for commercial vehicle fuel economy theory research and engineering analysis, provide theoretical basis and technical methods for commercial vehicle powertrain design and waste heat recovery and its application to commercial vehicle, also promote the improvement of energy efficiency and energy regeneration, and improve the technical level...