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Optimisation of hydrogen powered internal combustion engines (HYICE)

Final Report Summary - HYICE (Optimisation of hydrogen powered internal combustion engines)

The goal of the 'Optimization of the Hydrogen Internal Combustion Engine' (HYICE) project was to optimise a concept for an internal combustion engine (ICE) which has the potential to outdo both gasoline and Diesel engines with respect to efficiency and power density. For this purpose the two most promising principles of mixture formation, Direct Injection (DI) and Cryogenic Port Injection (CPI), have been studied.

The CPI aims for near-term economic drive trains, while, as a result of complexity and the large amount of calibrating parameters, DI offers the potential to exceed even the limits of CPI, however there is need for further fundamental research work.
To open up the whole potential of this outstanding fuel Hydrogen a dedicated, highly efficient ignition system has been developed. A commercial CFD-solver has been toughened up to the calculation with Hydrogen to support the development process also of future production engines. The models for mixture formation and combustion have been adapted and validated also by the use of optical equipment. In the USA the ICE is considered a valid option for Hydrogen-propulsion as well. To extract the maximum benefit out of efforts and investments made on both sides of the Atlantic Ocean an information exchange between automobile industry and researchers from Europe and the USA is arranged, ensuring the exchange of important and valuable know-how.

The investigations in HYICE evaluated the potential of Hydrogen high-pressure direct injection (HP-DI) concerning efficiency and power density. Specific advantages beneath the high power density are opened up by a wide field of possibilities for optimising the hydrogen combustion process. Only with high-pressure injection, the injection timing can be varied within a wide range and thus controlled fuel stratification can be realised. Within HYICE, extensive experimental work was carried out at TUG, employing a single-cylinder research engine in a modern passenger car configuration and a likewise transparent engine allowing insights into the mixture formation and combustion process. The best possible mixture preparation regarding efficiency could be pointed out with the definition of a perfect stratification. Further activities on improved injection strategies were carried out to approach this idealised benchmark stratification. By means of new injection strategies, thus controlling the combustion process, a method has been developed to significantly improve the noise behaviour which is of utmost importance in a passenger car application.

Within HYICE, the new 12.8l six-cylinder engine was specifically designed for Hydrogen operation. In a combined effort of 3D-CFD simulation at MAN and optical measurements at UBW and TUG, several injector nozzles were investigated and a suitable configuration for good homogenisation was found. By help of a turbocharger, a remarkable maximum power output of 200kW and an effective efficiency of 42% were achieved very quickly. The chosen lean burn concept still offers a lot of potential for further optimisation.

The design of all HYICE injectors is based on a proven gas valve concept of HVT. Throughout several injector generations most challenges could be solved. The solenoid actuator showed impressive performance concerning switching times. A needle bouncing effect during the closing phase has been observed but different approaches for low- and high-pressure DI injectors have already been performed by HVT in follow-up projects in order to solve this problem.

In contrast to direct injecting hydrogen engines, for the cryogenic port injection (CPI) the low pressure range of a liquid Hydrogen tank is sufficient. This concept takes advantage of the external mixture formation of Hydrogen and air by making use of the coldness. At the same time the concept of liquid Hydrogen storage and CPI forms a technically straightforward system, therefore supporting the attempt to build economic Hydrogen vehicles. Within HYICE detailed experimental investigation in the mixture formation and the combustion process, as well as validation and adaptation work on CFD tools have been combined into the development of a combustion system for CPI. The combustion process itself shows a very stable behaviour. Thus the CPI engine is predestined for operation with higher compression ratios - leading to a further increase in efficiency and turbocharging. With increased compression ratio an indicated efficiency of 44% has been demonstrated, further improvements may be expected. Turbocharged operation with extreme specific power output has also been investigated, whereby 100kW per litre of displacement have been reached.

The work on the H2-CPI engine was very successful and shows impressive results, the expectations have been partly exceeded and the challenges could mostly be solved. Moreover, the maturity of the injectors and the status of the development of the combustion system already prove the potential to apply them to a multi-cylinder engine for a first vehicle application.

A series of development topics that support the work on the different combustion systems have been summarised in an accompanying subproject. Within HYICE a very flexible and powerful ignition system has been developed, which is designed to combine high efficiency, high energy transfer to the gas and low heating of the electrodes in order to avoid hot-spots in the combustion chamber. For optimising the engine concepts as well as to support the development process of future production engines a suitable CFD solver is needed.

3D calculation models have been adapted to mixture formation and combustion by IFP and UBW, whereas the specific properties of Hydrogen were taken into account. These models were validated by data from literature and experiments and integrated into a solver, usable for the optimisation of gas exchange, mixture formation and the combustion processes. This Hydrogen proven CFD tool is a major result of the project, and it will be delivered by a commercial supplier, ensuring support and maintenance also in future upgraded versions. At UBW a mixing chamber test bed was designed and built up to gain detailed information about the turbulent mixture formation. Gas injections at different temperature and pressure levels can be performed. They are recorded by use of a Schlieren imaging system in combination with an electronic high speed camera. The great advantage of this system, compared e.g. to commonly used stroboscopic systems, is the capability to generate large data bases with high accuracy - important for averaging - and even more the possibility to observe typical behaviour of single injections like swirl generation and degeneration in series of consecutive images. At TUG, an optical engine was employed for these investigations. The visualisation of the mixture formation and combustion process was made possible by adapting the methods of Laser-Induced Fluorescence (LIF) and Raman-Spectroscopy for the use with Hydrogen. With this measurement method, for the first time detailed insights into the processes within a Hydrogen engine became possible.

The international cooperation between the European consortium members and Ford and its associates in the USA was intended to provide an interchange of know-how and thus accelerate the development of the Hydrogen engine. Within HYICE, Ford provided information on engine testing. With these results, important insights into the influence of different injector nozzle geometries and the compression ratio could be obtained. At the National Laboratories cooperating with Ford and funded by the US Department of Energy, research activities were carried out on fundamental questions concerning the Hydrogen combustion process. At ANL a research engine was employed which provides optical access through an endoscope, thus delivering insights into the engine even under critical high-load conditions.
The very ambitious Large Eddy Simulation (LES) modelling approach pursued by a research group at SNL had the goal of pointing out future potentials of an even more refined simulation. Due to its high computational expense, this work goes even beyond the targets of HYICE, giving an outlook to future possibilities of 3D-simulation of complex Hydrogen combustion processes.

In summary it can be ascertained that in the range of high-power vehicles, HYICE technologies can:
- Answer the customer's demand regarding both fuel efficiency and engine performance.
- Enable the development of products which can be sold at a reasonable price.
- Offer the chance of rapid dispersal of mass market Hydrogen vehicles, provided that the related infrastructure is available and that the political basic conditions are favourable.

Given the advantages and convincing properties of a Hydrogen driven reciprocating piston engine already to be observed today, it is generally expected that this engine will take on a firm position in the market and will be successful in the long turn, particularly in extra-urban traffic.

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