Here, the injection starts after inlet valve closing, which increases the charge density and avoids the possibility of back-fire resulting in an improved thermal efficiency. Another important point to be taken into account is the pre- or auto-ignition tendency of the hydrogen/air mixture in the manifold and during the suction stroke in the combustion chamber, which can lead to the risk of “back-fire” ( Yip et al., 2019).įor this reason, low-pressure direct-injection (LPDI) strategies turned into focus. This will decrease the volumetric efficiency, which results in a loss of engine power. However, due to its low volumetric energy density, the injection of hydrogen into the intake manifold replaces a significant part of air needed for the combustion. In addition, exhaust gas recirculation is used to reduce the combustion temperature and thus to decrease NOx formation. Typically, those engines are operated in a lean mode with a fuel–air ratio close to 0.5. Hydrogen induction can be realized by port fuel injection (PFI) where a premixed hydrogen–air mixture is aspirated or by direct injection (DI) into the combustion chamber.Īt this development stage, hydrogen PFI provides the best performance in terms of NOx raw emissions and engine operating stability. Hydrogen internal combustion engines are separated by both their injection and their ignition strategies. Due to its excellent specific energy density (e.g., more than three times as much mass specific energy compared to other fossil fuels), hydrogen is a suitable energy carrier and represents an important alternative to the use of electric drives. The CO 2 reduction goals come along with a further reduction of unburned hydro-carbons (HCs), particulate number (PN), carbon monoxide (CO), and nitrogen oxides (NOx). With regard to model year 2019, the CO 2 fleet emission must be reduced by −15% till 2025 and by −30% till 2030 ( Korn, 2020). Thus, the advantage of multi-hole guiding-devices is based on its flexible gas-jet orientation.īy the start of 2019, the European Union (EU) defined new emission targets for the commercial vehicle (CV) market. Here, it turns out that the volume increase does obviously not depend on the nozzle design. In a next step, the usage of spray-guiding devices to improve the global gas distribution during the injection period is discussed. This is shown by the comparison of spray propagation images that were observed with the Schlieren technique in a pressure vessel proving comparable spray properties. Furthermore, this contribution focuses on the usability of helium instead of hydrogen for the determination of spray properties. A metering technique for gas flow characterization and, for test simplification, a comparison of hydrogen with helium and nitrogen as possible surrogate gases indicate that helium and nitrogen can act as a substitute for hydrogen in functional testing. This contribution discusses deep injector analysis techniques with pneumatic and optical approaches for an improved overall understanding of functionality and effects caused by operation with a gaseous fuel. In terms of injector functionality, it must be ensured that the requested amount of hydrogen gas needs to be provided in time and, on the other hand, accurately metered to provide an appropriate mixing formation quality inside the combustion chamber. Especially when talking about direct hydrogen injection, the key challenge is to ensure a proper mixing between hydrogen and the combustion air-the mixing of gas with a gas is not trivial as shown in this article. For new hydrogen engine generations, there are different challenges concerning the injector layout and functionality. To achieve future emission targets for internal combustion engines, the use of hydrogen gas generated by renewable energy sources (known as “green” hydrogen) instead of fossil fuels plays a key role in the development of new combustion-based engine concepts. 2Chair of Powertrain Technologies, Technische Universität Berlin, Berlin, Germany. 1Department of Fuel Technology, TD-P2, IAV GmbH, Berlin, Germany.
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