Hoerbiger achieves diesel power parity with H2 system

AdaptH2 hardware (Photo: Hoerbiger)

In 2022, the then Diesel Progress International reported on the on-going development of hydrogen fuel injectors at Hoerbiger. Bernhard Zemann, head of the Engine Business Unit at the global tech company says that these are still under development, but moving towards series production.

“It’s directly related to the market,” he explains. “Fuel cells were always going to enter the market first, but that tech is not fulfilling demand in terms of mobility. [They are] not offering the robustness needed by some sectors. That is why we’re continuing to develop technology related to hydrogen internal combustion engines; when the market is ready for this technology, we will also be ready.”

While final work will soon be completed on the H2 injector technology, Hoerbiger and Altronic (a member of the Hoerbiger Group), in cooperation with Prometheus Applied Technologies, provider of hydrogen combustion system tech, are now advancing development of a solution for hydrogen ignition.

Bernhard Zemann (Photo: Hoerbiger)

With most other elements of the internal combustion engine carried over, including the cylinders, engine block, etc., it is the injectors and ignition system which are critical to successfully achieving the full potential of the H2 combustion process. With development of these units, Hoerbiger is leveraging its expertise in gas power to position itself as a specialist provider of the key components above the valve cover gasket supporting H2 combustion.

Zemann says that the H2 injector and ignition systems will be ready for market launch at the same time. “There was always the debate about hydrogen combustion, whether it was a viable solution. But this is done, we know it is a valid solution that can deliver the power and decarbonisation for heavy-duty engines.”

Overcoming power loss

From the outset of development it was already apparent that it would be impossible to convert a formerly diesel engine to use hydrogen fuel without a dedicated, specialised injector. The same is now being found with H2 ignition, which requires a system specifically engineered to initiate and control combustion within the very tight tolerances of the ultra-lean fuel mix.

“Two years ago, the question was ‘what is the minimum requirement to convert a diesel engine to use hydrogen’ and the answer was always the injector. It was the only change, in principle everything else could be carried over,” says Zemann.

But while it was possible to carry over those diesel-specific components, Zemann says that using hydrogen in such a setup resulted in 20 to 30% loss in power density and efficiency. “It was just an accepted loss,” he says ruefully. It was at this point the engineers at Hoerbiger started looking at making specific changes to how hydrogen fuel was ignited, with the goal of achieving power and efficiency parity with diesel.

“We found that the combustion system strategy has a bigger impact on power output than even the delivery of a fully homogenous air/fuel mixture coming from the injector,” explains Zemann.

To achieve that diesel/hydrogen power parity, engineers looked at patented gaseous-fuel engine technology. Developed in 2022, the process uses a controlled and predictive prechamber ignition model for the combustion process.

Engine efficiency using Prometheus combustion technology (Photo: Hoerbiger)

Zemann describes this combustion tech as a “nice to have” feature on engines using natural gas. But with hydrogen it’s not simply nice to have – it becomes critical to achieving efficiency across fuel usage and power output.

“It’s how you claim back that 20 to 30% in power density and efficiency,” he adds. “And this is how you get comparable performance to a diesel from a hydrogen combustion engine.”

Ignition is the key

Controlling variation in the starting point of the combustion process across each cycle is the key to controlling stability and thus achieving the required breakthrough to deliver equivalent power and efficiency. This is because fuel energy is not constant across the combustion process – instead, performance is determined during the spark event; it is the spark energy which must be adapted to achieve the desired combustion point.

In real time, this translates to a readjustment of the spark energy within 100 microseconds – or 100 millionths of a second. This energy adjustment compensates for the point on the electrode where the spark initiates, with the goal of maintaining the same point of combustion in each cycle.

“The measurement looks at whether the spark is on the leading edge or the trailing edge of the electrode, with respect to the direction of the flow,” explains Zemann. “Then a microprocessor determines the correct amount of spark energy needed to achieve the desired start of combustion, while preventing hot spots on the electrode which case combustion instabilities and shorter spark plug life.

“This all makes a substantional difference in gas engines, but not as much as it does in hydrogen-fuel engines. If there is a difference of one millimetre in the spark kernel travel time, that creates a completely different combustion scenario.”

If the spark is occurring on the trailing edge, that is closer to the open air/fuel mix and so does not need so much energy. Conversely, if the spark comes off the leading edge, this is further away and requires more energy to achieve the combustion starting point.

This levelling out of the combustion event sequence helps to prevent misfiring, knocking, etc., but also prevents heat build up across specific areas within the combustion chamber, another issue as this can cause premature combustion, efficiency losses and reduced power output.

Using an optimised combination of hydrogen injection, adaptive spark control based on advanced CFD of the combustion process, and spark plug design, the combustion instabilities associated with hydrogen can be eliminated and the higher power densities can be achieved.

With no trace of hyperbole, Zemann comments: “You need the ideal air/fuel mix from the injector, but combining that with this process gains back the 25% power loss of previous hydrogen engines due to misfire, while eliminating engine knock. The results are mind-blowing, it’s a revolution!”

Flow dynamic vortex

While managing the energy of the spark event is critical to gaining this diesel-like performance from a hydrogen internal combustion engine, there are other features which play a significant role.

Diagram of fuel mix in toroidal vortex (Photo: Hoerbiger)

One of these is the formation of a toroidal vortex. This donut shape, which is not dissimilar to that of a plasma ring in the tokomak of a fusion reactor, lends itself to rapid and complete combustion of the ultra-lean air/fuel mix. Complete combustion means there is no fuel residue remaining to unbalance the mix of the next injection event.

“This is why we have opted for a port injection architecture,” says Zemann. “The port system supports the correct diffusion angle and so delivery of the flow dynamic. It’s not a case of more energy, it’s all about the flow dynamic.”

To help deliver this, there is a miniature metal deflector in advance of the inlet valves which helps to direct the air/fuel mix and create a stable vortex which reduces cycle-to-cycle variation. By the time the new ignition unit reaches the market, this deflector will be incorporated into the body of the system.

The new ignition unit under development at Hoerbiger looks to have overcome some significant issues with using hydrogen as a fuel for internal combustion engines. And, unlike fuel cells which demand ultra-pure H2, virtually any hydrogen gas can be used. With the further benefit of decarbonisation, these types of technologies will make hydrogen a more attractive proposition in the market - when the market is ready.