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The adoption of a low-GWP refrigerant gas in MAC systems is mandatory from January 1st, 2017 according to the European Directive 2006/40/EC requirements for all new passenger cars, in order to gain their registration in the EU28 market. Following the work carried out in 2008 to support the FCA choice for the new types development, a further step was accomplished to evaluate the risk involved by the adoption of the low-GWP refrigerant gas R-1234yf in the MAC systems. This paper is focused on the activities held to enhance the 3D CFD method and its validation. In certain concentrations, R-1234yf could present a safety hazard to the vehicle occupants and, according to the ISO Standard Risk Scenario evaluation, 3D CFD tools are adopted to evaluate the ignition event associated with small or large leak in the passenger compartment. The method validation has been supported by both a simplified control volume “dummy cabin compartment” and an actual FCA vehicle.

Following the development of new technologies in Vehicle Thermal Management aiming to both enhancing the MAC System efficiency and reducing the thermal load to be managed, a prediction tool based on the AMEsim platform was developed at Advanced PD EMEA. This tool is dedicated to predict the effect of the implementation of sensors monitoring both the relative humidity and the carbon dioxide (CO2) concentration (taking into account passengers' generated moisture and CO2). This model implemented with the usual comfort inputs (CO2 and RH acceptable ranges) considers the system variables influencing the comfort and predicts the increase of both RH and CO2 concentration in the cabin compartment in any driving cycle depending on the number of occupants.

The subject addressed by this work, currently discussed in Europe following an European Commission inquiry, is the evaluation of the possibility to prevent the MAC (Mobile Air Conditioning) use below 18°C and its benefits in terms of CO2 emissions saving. This strategy, while providing an uncertain fuel consumption saving, has to be faced with basic safety and cabin comfort conditions. The OEMs (Original Equipment Manufacturers) may evaluate to address these concerns by controlling the cabin absolute humidity content. In order to maintain safety it should be acceptable to turn the AC on based on other inputs, such as air distribution modes (defrost or floor/defrost), windshield wiper usage, rear defroster usage, etc. FGA (FIAT Group Automobiles) exploited our proprietary prediction tool to assessing the yearly fuel efficiency that can be achieved in real use by means of the testing results of representative vehicles.

The European f-Gas Directive phases out HFC-134a from Mobile Air Conditioning systems (MACs) in new vehicles by 2017. In the US pending California and USEPA regulations have incentives to phase out HFC-134a earlier than 2017. As a result industry is striving to transform all global markets to a single new refrigerant in order to simplify global marketing. One of the global tools to help evaluate alternatives during this transition is the global LCCP (Life Cycle Climate Performance) and the development of the GREENMAC- LCCP© model. This model has become the global standard to measure the Life Cycle Analysis (LCA) greenhouse emissions of any proposed alternative refrigerant for MACs starting from bench test results and supporting the car manufacturer choice of the best suitable alternative refrigerant from an environmental perspective.

This paper deals with the application of a secondary cooling circuit to a turbocharged engine for a segment C car. The secondary coolant loop, working at low temperature, has been used to cool down the charge air by means of a coolant-to-air exchanger and as hot source of the HVAC circuit by means of a coolant-to-refrigerant condenser. The system is able to ensure both a constant air temperature at engine inlet, with smaller variations for different vehicle working conditions if compared to the normal production equipment, and a lower pressure at the condenser of the HVAC system, thus leading to a reduction in the fuel consumption of the vehicle. Starting from experimental measurements on MVEG cycle, an estimation of the fuel consumption reduction of the system in real use has been done using an LCCP tool FGA did develop and it is here presented.

The new F-Gas European Union (EU) Legislation requires car manufacturers to design their vehicles for application of low Global Warming Potential (GWP) refrigerant gasses. Low GWP substitutes to R-134a for Mobile Air Conditioning (MAC) application have to be assessed based on their potential for human exposure in terms of toxicity and flammability. Among the current potential candidates, the present paper deals with the flammability risk assessment of HFO-1234yf. This joint DuPont and Honeywell proposal is a Hydro-Fluoro-Olefin, 2,2,2,3 Tetrafluoroprop-1-ene.

In the framework of the activities for the selection of an alternate refrigerant to comply with the R-134a ban, FIAT chose to develop a carbon dioxide (R-744) MAC system on a vehicle representing the FIAT portfolio. The vehicle model was specifically selected to deal with two critical parameters in the low cost intermediate segment: a cabin compartment of comfortable size and a tiny engine compartment. The design target was therefore a MAC system featuring both a considerable cooling capacity and efficient packaging. The prototype was built with the most up to date version of R-744 components available, allowing the evaluation of advanced technology, resulting in meaningful results. General system and component specific issues are mentioned to explain the necessity of using additional components with respect to the typical R-134a MAC system (i.e. internal heat exchanger, accumulator, expansion device and externally controlled compressor).

The TxV model presented at the VTMS 5 has been improved with new experimental measurements. The model, inputted with the thermo-physical properties of the refrigerant at the orifice boundaries and the temperature conditions of the environment surrounding the bulb, allows to calculate the valve lift and the expanding fluid mass flow rate through the variable orifice. A good correspondence with the AC loop data measured during a cool-down test on a vehicle has been established and is here presented. The model allows therefore to seize the valve setting influence on the mass flow rate, giving a solid tool to automotive engineers in exploiting usefully the AC loop simulating tools which adopt the presented model to choose the correct components in both development and problem solving for the current market's good at first shot challenges.

The current A/C system performance prediction codes usually describe the TXV behaviour in terms of SH dependence on the evaporation pressure. The data currently issued by TXV suppliers give the maximum outlet evaporator pressure values at 0 °C and 10 °C outlet evaporator temperature (Fig. 1).