On the way to fuel-cell-vehicle (FCV) commercialization Volkswagen has developed several generations of prototype-FCV. The latest prototype called HyMotion3 has a freeze-start capability to at least -15 deg C (prediction), is equipped with 700 bar gaseous-hydrogen-tank technology and has 100 kW of driving power. Further the fuel-cell system (FCS) comprises an active hydrogen-recirculation and a gas-to-gas-humidification on the cathode-side. The drive train consist besides the FCS of a high-power Li-ion battery to recapture braking energy and to boost energy while accelerating. Using today's PEM-FCS for automotive transportation, the cooling-system is one of the most limiting factors in order to achieve appropriate driving conditions since FC-temperature is limited to about 90 deg C. Especially considering steep uphill driving with high loads at raised ambient temperatures such as 40 deg C lets the cooling-temperature easily exceed the upper limit, where the FC can not permanently be operated without increasing degradation. Therefore Volkswagen's long-term- goal is to build FC with higher operating-temperature (such as 120 deg C and higher). This talk offers a description of how the cooling-system for the latest prototype-FCV HyMotion3 was optimized. As instruments for this optimisation a stationary 1D-fluid-simulation of airflow which requires measurements in a climate wind-tunnel as well as a CFD-calculation of front vehicle package are used. In order to describe the airflow rate of the radiator, the pressure-loss curves of every component such as the radiator itself, the AC-condenser as well as the air louvers have to be determined by measurements in a wind-tunnel test-bench. Further the pressure gain of the fans is measured for different rotational speeds. In addition the heat-transfer-characteristic of the radiator has to be determined for different airflow und waterflow rates and temperature-differences. These curves are entered in a 1D-fluid-calculation-tool called KULI, which besides these curves takes the position and geometrical dimensions of the components into account. The most important and yet unknown variable is the build-in resistance of the front-end airflow, which comprises the pressure loss of the FCS in the front vehicle. To determine the optimum of radiator-depth, this build-in resistance is approximated as an empirical value taking front end package into account. A parameter-variation offers the optimum radiator-block-depth where most heat is rejected. After building up the FCV, measurements to validate the estimate of build-in resistance are made in a climate wind-tunnel.
Optimization of a fuel-cell-cooling-system for automotive transportation at Volkswagen
Optimierung eines Brennstoffzellenkühlsystems für Autos bei Volkswagen
2007
5 Seiten, 5 Bilder
Aufsatz (Konferenz)
Englisch
Brennstoffzelle , Unternehmen , Automobil , Temperatur , Druck (Mechanik) , Wasserstoff , Antriebsleistung , Rückführung , Wasserfeuchtung , Kathode , Lithiumbatterie , Kühlsystem , Betriebstemperatur , Simulation , Luftströmung , Windkanalprüfung , numerische Strömungssimulation , Kühlerlüfter , Druckverlust , Optimierung , Kondensor , Gebläse , Wasserströmung , Umdrehungsgeschwindigkeit , Wärmeübertragung , Temperaturdifferenz
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