|H2BVplus hydrogen combustion engine. Click to enlarge.|
The BMW Group Forschung und Technik, in cooperation with researchers in Graz and Vienna, Austria, has developed a dedicated (i.e., monovalent) hydrogen combustion engine with diesel-like geometry and progressive H2 high-pressure direct-injection technology. The result is an efficiency level of up to 42%, on par with that of the best turbodiesel engines.
The “H2BVplus” project is aimed at investigating a hydrogen self-ignition combustion process. Current hydrogen combustion engines are spark-ignited. Sponsored by Austria’s Federal Ministry for Transportation, Innovation and Technology (BMVIT), project partners include BMW, the Institute for Internal Combustion Engines and Thermodynamics at Graz University of Technology, HyCentA Research GmbH in Graz, as well as HOERBIGER ValveTec GmbH in Vienna.
A combustion system employing hydrogen self-ignition opens up new opportunities concerning both efficiency and power output for alternative automotive propulsion systems.
High efficiency is targeted in H2 vehicles on economic and energy grounds, as well as to minimize the space required for the fuel tank. The need for high power density is better satisfied in a hydrogen engine due to the excellent ability for turbocharging, especially compared to spark-ignited engines, given that combustion anomalies such as knocking and backfiring may be ruled out. An additional and significant increase in compression ratio is possible.
The absence of a particulate emission limit, which forces conventional diesel-type engines to be operated at lean mixture, allows for operation at a stoichiometric air/fuel ratio to provide both maximum mixture calorific value and, subsequently, mean effective pressure (BMEP). The injection of hydrogen within the high-pressure phase of the engine cycle additionally boosts BMEP.
In terms of compression ratio, efficiency and consequently vehicle operating range, the self-ignition combustion system is expected to be superior to actual H2 -Otto-type IC engines. The project earlier was able to realize some self-ignited operating points with induction air heating assistance and an increased compression ratio on an Otto-type research engine inherited from earlier H2-related projects, and also to devise promising layouts for combustion chamber and injector nozzle geometries via the extensive use of 3D CFD simulation tools. Based on these design proposals, the completely new diesel-type research engine and the related high-pressure injection units were realized in hardware.
The main challenge for a combustion of hydrogen with self-ignition is the high auto-ignition temperature. Other challenges include maximum pressure increases and ignition pressures, the impact of high EGR rates and NOx formation rates.
The newly developed combustion system combines the strengths of spark-ignition and diesel concepts, while utilizing the favorable combustion properties of hydrogen to achieve the efficiency values.
The engineers based their work on the joint EU “HylCE” project, during which maximum specific powers of up to 100 kW per liter of displacement were demonstrated for a spark-ignition hydrogen combustion process.
|3D-CFD simulation of hydrogen high-pressure injection. Click to enlarge.|
Engineers from the BMW Group Forschung und Technik developed a new cylinder head for hydrogen operation based on a production diesel engine. The combustion chamber of the engine was configured jointly by BMW and the Graz University of Technology using numerical flow simulation. HOERBIGER ValveTec GmbH designed high-pressure injectors for direct injection of hydrogen into the combustion chamber with pressures of up to 300 bar (30 MPa or 4,351 psi). These injectors were tested and calibrated at the Hydrogen Center Austria, which also provided the hydrogen infrastructure.
|H2BVplus HOERBIGER hydrogen high-pressure injectors. Click to enlarge.|
Extensive test runs on the test benches of the Institute for Internal Combustion Engines and Thermodynamics of the Graz University of Technology have shown that a combination of spark-ignition and diesel combustion systems using surface ignition subsequently followed by a diffusion type of combustion is the ideal solution with respect to engine efficiency. As a result, the entire characteristic engine map range of a typical passenger car engine can be covered and top level efficiency values are achieved.
Attendant benefits are the increase in specific power and reduction of fuel consumption. Thus, even in an early concept phase, this combustion system matches the efficiency values of the currently best turbodiesel engines at a maximum of 42%. As the exhaust gas heat of internal combustion engines can be used well due to the high temperature levels, further increases in overall efficiency will be possible in the future as a result of waste heat utilization.
BMW Forschung und Technik GmbH is a 100% subsidiary of BMW AG and has been responsible for research within the BMW Group since 2003. Its subject areas cover Vehicle Technology, Clean Energy (hydrogen technology), EfficientDynamics (intelligent energy management/alternative drive systems), ConnectedDrive (driver assistance/active safety) and IT Drive (IT and communications technology).
HOERBIGER ValveTec GmbH is a company of the HOERBIGER Group. HOERBIGER is active throughout the world as a leading player in the fields of compression technology, automation technology and drive technology. The focal points of its business activities include key components and services for compressors, gas-powered engines, and turbomachinery, hydraulic systems and piezo technology for vehicles and machine tools, as well as components and systems for shift and clutch operations in vehicle drive trains of all kinds.
The core objective of the Institute for Internal Combustion Engines and Thermodynamics at the Graz University of Technology is to carry out innovative and internationally recognized teaching and research within the interrelated fields of energy, engine, transport and environment, and in particular to contribute to solving environmental problems.
The HyCentA (Hydrogen Center Austria) promotes the use of hydrogen as a regenerative energy carrier. With its hydrogen test center and the first hydrogen delivery station in Austria, the HyCentA acts as a focal point and information platform for hydrogen-oriented research and development activities.