Hydrogen propulsion moved from rockets to racers this week as BMW set nine new speed records for hydrogen powered automobiles. The record attempt was conducted at the high-speed Miramas Proving Grounds in France, where the 210kW hydrogen prototype proved BMW's point that hydrogen can replace conventional fuel without a performance compromise.
The H2R Record Car uses a six-litre 12 cylinder power unit and accelerates to 100 km/h in approximately 6 seconds with a top speed of 302.4 km/h (185,52 mph). Based on the 760i power unit, the main modifications involved the fuel injection system being adapted to the special requirements of hydrogen.
The testbed is helping in the development of a dual-mode BMW hydrogen-petrol engine for its premium saloon 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 H2R prototype set up a raft of speed records for the new class, from a standing-start quarter mile (14.933 seconds at 96.99 kmh) and a flying kilometre at 300.19 kmh.
BMW's motive in setting up these records was not only to prove the power and performance the hydrogen engine is able to offer.
Rather, the reliability and durability of the technology used clearly demonstrates the supremacy of BMW in developing the hydrogen engine to production standard.
In this process BMW is concentrating on the combustion engine, simply because the combustion power unit, given the sum total of all its features and characteristics, still offers the largest number of advantages and benefits all in one.
The BMW H2R Record Car was conceived, designed and developed by BMW Forschung und Technik GmbH, the legendary subsidiary of BMW AG.
The name "H2R" stands for "H two Race Car", "Hydrogen Record Car" or "Hydrogen Research 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 unproblematic and straightforward adaptation for the record car.
Second, the development specialists were able in the development process to use proven BMW chassis and suspension systems naturally meeting the strictest requirements.
And third, consistent, far-reaching use of CAD technology allowed a clearly oriented and time-saving development process.
The "heart" of the H2R Record Car is based by and large on BMW's top-of-the-range power unit, the Company's six-litre 12 cylinder. 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 in 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.
And it is worth noting in this context that this need to cope with a lower level of lubrication already arose in the past when introducing unleaded gasoline, production engines since then being built with even stronger and more resistant materials.
A fundamental consideration is that 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 not being ignited until the piston reaches top dead centre, 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 naturally requires a great deal of attention outside of the combustion chamber.
To avoid misfiring, for example, BMW's engineers have developed a specific gas cycle and injection strategy, with BMW's VANOS infinite camshaft adjustment masterminding the share of residual gas according to specific, on-demand requirements.
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.
The VALVETRONIC variable valve timing on the 12 cylinder offered 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 consistently 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.
A further point is that the valves have to cover a far wider range of different features and 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 also find on a state-of-the-art gasoline engine, the mixture 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 is just as powerful as a conventional gasoline-engine car, while at the same time its 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 ensures 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 - recognise 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 aluminium spaceframe as well as the entire chassis and suspension system. High-strength aluminium structure panels using the advantages of aluminium 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 an absolutely excellent, direct 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, aluminium track control arms, a tiebar, and an anti-roll bar. The front axle subframe is formed by a welded aluminium 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 aluminium 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-dimensional 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 tyres measuring 245/40 x 19.
BMW's designers have also given the H2R Record Car a truly unique body: Measuring 5.40 metres in length and 2 metres 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 metres and the drag coefficient is a mere 0.21.
At the rear a 20-centimetre-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-fibre-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.
