BMW Shows Demonstration Mono-Fuel Version of the Hydrogen 7; Next Engine Version Will Use Charging for 2-3X Increase in Power Density
BMW introduced a new mono-fuel version of its Hydrogen 7 vehicle at the 2008 National Hydrogen Association Conference in Sacramento, CA today. The BMW Hydrogen 7 mono-fuel is a demonstration production vehicle, not a prototype, and was created to showcase the zero CO2 and low emissions potential and feasibility of a dedicated hydrogen internal combustion engine (ICE).
Based on the BMW Hydrogen 7 bi-fuel version (gasoline and hydrogen) (earlier post), the BMW Hydrogen 7 mono-fuel is equipped with a 6.0-liter V12 internal combustion engine (ICE) which has been engineered to run exclusively on hydrogen. The hydrogen storage system in the mono-fuel version is the same as in the bi-fuel version: a cryogenic tank that holds approximately 8 kg (17.6 lbs) of liquid hydrogen.
The hydrogen engine uses fully variable VALVETRONIC valve management and variable double-VANOS camshaft control. Hydrogen is delivered with a hydrogen supply pipe integrated in intake manifold. Under full load, the engine runs under stoichiometric conditions: a complete balance of oxygen and hydrogen (lambda = 1). This mixture ratio also provides the highest level of performance and output on low emissions in the hydrogen mode.
Although unlike fossil fuels, the combustion of hydrogen generates neither hydrocarbons (HC) nor carbon monoxide (CO), it does produce NOx at high combustion temperatures. To reduce NOx, the Hydrogen 7’s engine runs with a lean burn under partial load (lambda > 2). The lean burn keeps temperatures in the combustion process are relatively low, keeping NOx emissions to a minimum.
Such a lean burn mode can be maintained throughout a particularly wide range of operation in the engine control map. And since hydrogen offers particularly broad ignition limits and burns at a fast rate, only a small amount of fuel is required in the mixture to generate a high level of efficiency, according to BMW. As the engine moves to a richer burn to boost engine output (reaching a max of lambda = 1), the engine management system helps to reduce the engine-out NOx. Remaining NOx is handled by a regular three-way catalyst.
Compared with the bi-fuel version, this vehicle achieves lower emissions, and slightly increased engine performance, reduced consumption and greater hydrogen range (140 miles versus 125 miles).
The Hydrogen 7’s V12 mono-fuel ICE produces no CO2 and near-zero emissions, as recent testing by Argonne National Laboratory (ANL), confirmed. ANL conducted emission tests on BMW Hydrogen 7 mono-fuel vehicles in early March 2008.
The mono-fuel Hydrogen 7 will also appear at the upcoming 2008 SAE World Congress in Detroit, MI (14 - 17 April). BMW and ANL will hold a joint press conference about the results of the emission testing at the event.
Next steps. The next step for BMW, which is maintaining its focus on the hydrogen combustion engine as a solution for almost zero emission vehicles, is to develop a charged version of the engine. According to Tobias Brunner of BMW, who also discussed BMW’s approaches to hydrogen storage at the NHA conference, shifting to a charged engine with about 8-10 bar of pressure will increase the power density of the hydrogen engine by between two to three times: from a density of 33 kW/liter in the current mono-fuel V-12 to a density of between 70-90 kW/liter in the future engine.
The charged engine will be applied in a smaller vehicle than the 7 Series model, and will likely be paired with a cryo-compressed hydrogen storage system (CcH2), assuming development and proof-of-concept work on those systems proceeds according to plan.
Cryo-compression is one of the approaches being pursued to increase the gravimetric and volumetric storage capacities of compressed gas tanks from their current levels. At fixed pressure and volume, gas tank volumetric capacity increases as the tank temperature decreases. Cooling a tank from room temperature to liquid nitrogen temperature (77 K) will increase its volumetric capacity by a factor of four, although system volumetric capacity will be less than this due to the increased volume required for the cooling system.