BMW H2R Hydrogen Racecar
Hydrogen does not only mean top performance in rockets traveling to outer space: BMW has proven what the hydrogen car is capable of, setting 9 records for cars powered by a hydrogen-fuelled internal combustion engine. "Nine records marking the start into the hydrogen age. BMW technology has already come a long way. Now, together with politicians and the energy industry, we must turn our vision of sustained mobility into reality", stated Professor Burkhard Göschel, Board Member of the BMW Group, during the speed record trials in Miramas. Achieving this amazing success at the high-speed Miramas Proving Grounds in France, the BMW Group has clearly proven its conviction that hydrogen is able to replace conventional fuel without requiring the driver to compromise dynamic performance.
The specifications of the H2R Record Car are a testament to this possibility. The 6-liter V12 engine develops an output of more than 210 kW or 285 bhp. This engine propels the BMW prototype to 100 km/h in approximately 6 seconds and gives it a top speed of more than 302.4 km/h (185.5 mph). Based on the gasoline power unit featured in the BMW 760i, BMW's hydrogen combustion engine boasts the most advanced technologies such as BMW's fully variable VALVETRONIC valve drive.
The main modifications to the engine involve the fuel injection system adapted by BMW to the special attributes and requirements of hydrogen. The H2R Record Car benefits from the results gained in series development of BMW's future hydrogen engine for the world's first premium sedan built for dual-mode operation.
BMW will launch a dual-mode version of the current 7 Series during the production cycle of the present model, thus introducing the first car of its kind able to run on both hydrogen and gasoline.
The BMW H2R Record Car was conceived, designed and developed by BMW Forschung und Technik GmbH, the legendary subsidiary of BMW AG. The expressive, purposeful exterior design was created by DesignworksUSA, the California-based strategic design consultancy owned by BMW Group. The name H2R stands for Hydrogen Record Car.
"We had just 10 months to develop the H2R prototype", states Jürgen Kübler, the H2R Project Manager. But a short time span like this is quite normal for the creative engineers that make this Company so very special.
In the process the engineers and development specialists were of course supported by three factors: First, the components featured in BMW's hydrogen production car of the future have now reached a high degree of maturity allowing their straightforward adaptation for the record car. Second, the development specialists were able, in the development process, to use proven BMW chassis and suspension systems which matched the strict requirements. And third, far-reaching use of CAD technology allowed for an effective and efficient development process.
The "heart" of the H2R Record Car is based by and large on BMW's top-of-the-line power unit, the Company's 6.0-liter V12. It is able to run on hydrogen fuel through the adjustment of engine management as well as the fuel/air mixture formation components.
The most significant differences in terms of the engine's structural components are the hydrogen injection valve and the choice of materials for the combustion chambers: Contrary to the production engine with fuel injected directly into the combustion chambers themselves, the injection valves in the hydrogen engine are integrated into the intake manifolds. And for the specific speed record requirements to be fulfilled in this case the hydrogen combustion engine was designed and built for single-mode operation, running exclusively on hydrogen.
This allowed the engineers to set up and tune the engine specifically for hydrogen requirements, for example by using special valve seat rings made of an appropriate material. The reason for this necessity is that hydrogen does not have the lubricating effect of a conventional gasoline/air mixture. It is worth noting in this context that this need to cope with a lower level of lubrication has come up before. With the introduction of unleaded gasoline, production engines have been built with even stronger and more resistant materials.
The combustion properties of hydrogen are quite different from those of gasoline or diesel: While hydrogen burns faster than conventional fuels under normal air pressure, the combustion temperature is slightly lower than in the case of gasoline.
Inside the engine the high combustion speed of the hydrogen/air mixture generates a higher temperature than in an engine running on gasoline. Engine management of the BMW H2R Record Car has been modified accordingly. The hydrogen/air mixture is not ignited until the piston reaches top dead center, thus ensuring maximum output. With a gasoline/air mixture burning relatively slowly, by comparison, the mixture must be ignited at an increasingly early point as a function of engine speed, the pressure peak thus being reached just as the piston starts to move down.
A significant advantage of the higher combustion pressure of the hydrogen/air mixture is that the generation of more power from the same amount of energy means a higher degree of efficiency.
As desirable as the high standard of ignitability of hydrogen within the engine may be, it also requires a great deal of attention outside of the combustion chamber.
Before the hydrogen/air mixture is able to flow into the cylinders, the combustion chambers are cooled by air to ensure that the fuel/air mixture is not able to ignite in an undesired, uncontrolled process.
Exclusive to BMW, VALVETRONIC technology serving as a standard feature to mastermind the valves on the 12 cylinder gives the Company's engine development specialists an ideal tool for controlling this demanding gas charge cycle. VALVETRONIC controls not only the duration of valve movement, but also the actual valve lift. This effect is provided by an intermediate lever between the camshaft and the two intake valves on each cylinder infinitely modified in its position relative to the camshaft by an additional eccentric shaft operated by an electric motor. Depending on the position of this eccentric shaft, the lever transforms the "hump" on the cams into a larger or smaller valve movement.
VALVETRONIC is based on BMW's infinite camshaft adjustment process. Already well-known under its trade name VANOS, this system is an integral part of the VALVETRONIC concept. Incorporating a hydraulically controlled adjuster unit in the camshaft drive, VANOS modifies the beginning and end of the valve opening period, fully variable valve management serving to adjust the gas charge cycle in the 12 cylinder power unit perfectly to the requirements and characteristics of hydrogen drive.
With hydrogen being injected into the intake manifold as late as possible, the injection valves have to meet very demanding requirements. Hence, the valves are a trendsetting new development for BMW. And since gaseous hydrogen takes up a larger volume per unit of energy than liquid gasoline, the hydrogen injection valves are larger than conventional injection valve units.
In addition, the valves have to cover a far wider range of different requirements, operating under all kinds of system pressure levels and with injection periods ranging from very short to relatively long. One of the main objectives in developing the valves was to inject exactly the right amount of hydrogen required into the intake manifold within a very short time-frame at very high engine speeds and under full load.
Under full load the 12 cylinder power unit runs on a fuel/air mixture of lambda = 1. This is exactly the same mixture we find on a state-of-the-art gasoline engine and one which, in principle, offers the highest and most efficient power output in a combustion engine. Under part load - again a significant benefit offered by hydrogen - the engine runs efficiently in the lean burn mode with surplus air.
Under specific conditions, that is with a specific fuel/air mixture, the combustion of hydrogen leads to the generation of nitric oxides. This mixture "slot" starts slightly above lambda = 1 and extends to the range of lambda > 2.
The simple solution to this problem is to leave out this mixture "window" altogether, since it is not required for running the engine. Hence, the fast management system controlling the BMW hydrogen engine skips this operating range completely, thus avoiding NOx emissions in the process. As a result, the H2R Record Car?s emissions are limited, for all practical purposes, to nothing but steam.
The fuel system featured in the BMW H2R Record Car is based on a proven series development concept. Fuel is filled into the tank of the H2R prototype at a mobile hydrogen filling station through a manual tank coupling. The vacuum-insulated, double-walled tank has a capacity of more than 11 kilos of liquid hydrogen and is fitted next to the driver's seat. A total of three valves ensure optimum safety, the operating valve on the tank opening at a pressure of 4.5 bar.
Two additional safety valves rule out any dangerous consequences of possible leaks in the jacket around the tank serving to keep the hydrogen at the low temperature required, opening up as soon as pressure within the tank exceeds the limit of 5 bar. This double-redundant safety system guarantees optimum safety at all times, ensuring that the hydrogen tank will not burst as a result of excess pressure.
Gas pressure builds up in the fuel supply system simply because of the rising temperature of the cryogenic, liquid hydrogen in the tank and is kept at an operating pressure of approximately 3 bar by a tank pressure controller. Then the coolant running within the 12 cylinder power unit warms up the hydrogen gas in a heat exchanger to ambient temperature.
Additional valves monitor the pressure of gas in the fuel pipes leading to the engine: Cold low-temperature valves inside the tank control the removal of hydrogen from the tank itself. Should any of the pre-flow pipes develop a leak, with supply pressure dropping below 0.4 bar, the fuel supply valves close automatically, disconnecting and sealing the tank off from its surroundings. The supply pipe can also be interrupted manually by an interruptor tap.
To maintain optimum supply pressure on the injection valves at all times ? especially as this pressure may vary as a function of driving conditions ? engine management reduces pressure in the supply pipe to approximately 1.2 bar by means of a control valve fitted specifically for this purpose.
This comprehensive safety system featured in the H2R Record Car is supervised additionally by a telemetric system of the same type as in Formula 1. Four hydrogen sensors fitted at neuralgic points - for example in the tank itself and around the tank coupling - recognize any leakage immediately and inform the driver accordingly.
Focusing on the structure and chassis of the BMW H2R Record Car, the engineers and development specialists at BMW Forschung und Technik GmbH used series components carried over from a sophisticated, thoroughbred BMW sports car: the monocoque aluminum spaceframe as well as the entire chassis and suspension system. High-strength aluminum structure panels using the advantages of aluminum as a particularly light material resistant to corrosion fill in the open spaces between the extra-large extrusion-pressed profiles giving the car its stable "skeleton".
The result for the driver is a very stable driving experience without the slightest vibration or body "tremble".
The front suspension is based on a double-wishbone spring strut front axle together with rack-and-pinion steering, aluminum track control arms, a tiebar, and an anti-roll bar. The front axle subframe is formed by a welded aluminum structure made up of extrusion-pressed profile bars and plates holding all front axle components and bolted to the body at six points. The track control arm made of forged aluminum comes complete with two ball joints in the interest of precise wheel guidance and directional stability.
Wheel guidance and stability at the rear is provided by an integral four-link axle, a multi-arm principle patented by BMW and rounded off in this case by an anti-roll bar. Optimum road contact and safety, finally, is ensured by tires measuring 245/40 x 19.
The designers have also given the H2R Record Car a truly unique body: ?We wanted to embrace the aerodynamic requirements we defined in the wind tunnel with a form language that was appropriate to the purpose of the car; the results are a true expression of the car's functional requirements and objectives to be clean, fast, and uniquely BMW," said Michael Scully, Senior Designer of DesignworksUSA , who combines his intense involvement in motorsports with the intellectual and aesthetic challenges of multidisciplinary design.
Measuring 5.40 meters in length and 2 meters in width, the body of the car is designed through and through for optimum streamlining. And to reach record speeds, the frontal area measures just 1.85 square meters and the drag coefficient is a mere 0.21. At the rear a 20-centimeter-long diffuser prevents air swirl behind the car, which might potentially slow it down.
The side profile and sheer length of the H2R prototype also serve to ensure stable driving characteristics at very high speeds. Like on a Formula 1 racing car, the outer skin is made of carbon-fiber reinforced plastic offering the optimum combination of superior stiffness and low weight: Overall weight of the H2R with a full tank and the driver at the wheel is 1560 kg or 3440 lb.
Source: BMW press