Harnessing hydrogen

May 30, 2023

A new gas injector system design has made it possible to inject hydrogen directly into a vehicle's combustion chamber.

Like all internal combustion engines (ICEs), zero-emission hydrogen engines require a mixture formation system for metering fuel, in this case hydrogen gas. Currently, the most promising approach is a low-pressure direct injection (LP-DI) system, which injects the fuel directly into the engine's combustion chamber. If injection is only allowed to start after the intake valves has closed, undesirable air displacement can be avoided and torque can be increased by around 20% at the same boost pressure of simple duct injection systems.

However, the low density of hydrogen requires comparatively large opening cross sections to blow the gas into the combustion chamber in the available time window, and presently there are no mass-produced LP-DI injectors that can meet the required specifications in the long-term.

Led by Professor Karsten Wittek, researchers from the Heilbronn University of Applied Sciences are seeking to change this, having developed a novel LP-DI system for gaseous fuels that makes it possible to inject hydrogen directly into the combustion chamber.

"Using hydrogen as an energy source in a vehicle has the advantage over a battery that the vehicle can be refuelled much faster than a battery can be charged," Wittek says. "The hydrogen fuelled ICE is slightly less efficient than a fuel cell system, but an ICE vehicle is much less complex and less expensive than a fuel cell vehicle, and is the more robust system."

The design is based on an inward opening nozzle with a seat seal that is actuated servo-pneumatically and uses the pressure energy of the inflowing fuel gas. The design of the seat geometry in combination with highly wear-resistant ceramic materials guarantees compliance with the demanding service life requirements of various industrial applications, particularly the large engines of heavy commercial vehicles, construction machinery and locomotives.

"In those applications where the average power demand is high, the efficiency gap between the ICE and the fuel cell gets very small," Wittek explains. "Heavy commercial vehicles are often operated at high power output, thus the fuel cell does not consume significantly less fuel when compared to a hydrogen-fuelled ICE vehicle. Another point is that a hydrogen ICE can easily achieve the lifetime of a present day diesel truck engine without any degradation in power and efficiency over its lifetime. How far fuel cell trucks and battery trucks might achieve this still needs to be found out."

Although realised as a prototype for now, extensive tests were completed on the injection nozzle test bench and engine test bench to confirm the system delivered all relevant functional properties. A patent has since been filed for the invention. According to Wittek, now that his team's hydrogen injection system has undergone a first prototype phase, the next step is to carry out further development in cooperation with an unnamed Tier 1 supplier.

Regarding how the system could be realistically implemented in future, he explains: "Existing diesel engines of on and off-road vehicles could be retrofitted with moderate effort, particularly regarding changes to the engine. The hydrogen tank system is the biggest issue when retrofitting a vehicle. In a truck, the hydrogen storage tanks will be mounted behind the cabin."