Holistic Thermal Energy Modelling for Full Hybrid Electric Vehicles (HEVs)

Full hybrid electric vehicles are usually defined by their capability to drive in a fully electric mode, offering the advantage that they do not produce any emissions at the point of use. This is particularly important in built up areas, where localized emissions in the form of NOx and particulate matter may worsen health issues such as respiratory disease. However, high degrees of electrification also mean that waste heat from the internal combustion engine is often not available for heating the cabin and for maintaining the temperature of the powertrain and emissions control system. If not managed properly, this can result in increased fuel consumption, exhaust emissions, and reduced electric-only range at moderately high or low ambient temperatures negating many of the benefits of the electrification. This paper describes the development of a holistic, modular vehicle model designed for development of an integrated thermal energy management strategy. The developed model utilizes advanced simulation techniques, such as co-simulation, to incorporate a high-fidelity 1D thermo-fluid model, a multi-phase HVAC model, and a multi-zone cabin model within an existing longitudinal powertrain simulation environment. It is shown that the final model is useful of detailed analysis of thermal pathways including energy losses due to powertrain warm-up at various ambient temperatures and after periods of parked time. This enables identification of sources of energy loss and inefficiency over a wide range of environmental conditions. </div

Modelling and Co-simulation of hybrid vehicles: A thermal management perspective

Thermal management plays a vital role in the modern vehicle design and delivery. It enables the thermal analysis and optimisation of energy distribution to improve performance, increase efficiency and reduce emissions. Due to the complexity of the overall vehicle system, it is necessary to use a combination of simulation tools. Therefore, the co-simulation is at the centre of the design and analysis of electric, hybrid vehicles. For a holistic vehicle simulation to be realized, the simulation environment must support many physical domains. In this paper, a wide variety of system designs for modelling vehicle thermal performance are reviewed, providing an overview of necessary considerations for developing a cost-effective tool to evaluate fuel consumption and emissions across dynamic drive-cycles and under a range of weather conditions. The virtual models reviewed in this paper provide tools for component-level, system-level and control design, analysis, and optimisation. This paper concerns the latest techniques for an overall vehicle model development and software integration of multi-domain subsystems from a thermal management view and discusses the challenges presented for future studies

Characterisation of aerosol combustible mixtures generated using condensation process

An accidental release of a liquid flammable substance might be formed as an aerosol (droplet and vapour mixture). This phenomenon might be due to high pressure sprays, pressurised liquid leaks and through condensation when hot vapour is rapidly cooled. Such phenomena require a fundamental investigation of mixture characterisation prior to any subsequent process such as evaporation and combustion. This paper describes characterisation study of droplet and vapour mixtures generated in a fan stirred vessel using condensation technique. Aerosol of isooctane mixtures were generated by expansion from initially a premixed gaseous fuel-air mixture. The distribution of droplets within the mixture was characterised using laser diagnostics. Nearly monosized droplet clouds were generated and the droplet diameter was defined as a function of expansion time. The effect of changes in pressure, temperature, fuel-air fraction and expansion ratio on droplet diameter was evaluated. It is shown that aerosol generation by expansion was influenced by the initial pressure and temperature, equivalence ratio and expansion rates. All these parameters affected the onset of condensation which in turn affected the variation in droplet diameter

Sensitivity analysis and calibration of vehicle HVAC

Due to the non-uniformity of material properties and the complexity of the airflow regimes within automotive passenger compartments, modelling their thermal dynamics is a challenging task that requires the application of hardware demanding computational tools and methods - FEA & CFD. Evaluation of the average thermal conditions of a cabin compartment can be achieved by using simpler, computationally friendly methods like the 1D CFD simulation technique. A two-zone GT-Suite cabin compartment model capable of predicting the average thermal conditions during various drive cycles has been created. The cabin model is based on a conventional SUV. A sensitivity analysis was carried out to identify the parameters with a significant impact on the cabin thermal response. The cabin model has been calibrated and validated with thermal performance test data. The validated cabin model and a 1D CFD refrigeration circuit model, have been integrated into the baseline HVAC system model. The baseline HVAC system performance has been validated against climate chamber physical test data. A theoretical performance comparison between the baseline HVAC system and an electrified HeVAC system have been carried out. The key difference between the systems is that the HVAC system uses a conventional mechanically driven swashplate compressor and the HeVAC system uses a high-efficiency electric scroll compressor. The CoP and the cabin thermal response have been evaluated for both systems. The 1D CFD model can be implemented in complex vehicle models running on multiple software domains via co-simulation.</p