Hydrogen – making combustion engines green

“How many events did we have today?” asks Andrea Prospero on arriving at the test stand early in the morning. “Just a few – things are progressing,” answers his colleague Rudi Hoff. The two men are developers at Rolls-Royce, working as part of an interdisciplinary team to develop the first hydrogen combustion engine for a company which until now has been famous for its diesel and gas engines. And ‘events’ are a big part of this.  

Hydrogen combustion = major challenge

“Put simply, an 'event' is where the hydrogen-air mixture in the cylinder ignites too early,” reveals Rudi Hoff. He has spent the past two years working on hydrogen combustion in great detail and counts it as a major challenge because hydrogen is extremely flammable. Even with just a small amount of it in the air, a tiny spark is enough to ignite the mixture. The engineers already had experience of mtu gas engines, on which the new hydrogen units are based, but say there are major differences regarding combustion in particular.    

First mtu hydrogen engines to ship in 2024

The challenges must now be resolved over the coming months because the first two mtu hydrogen engines are scheduled for delivery in just one year's time (January 2024). They are due to be used in combined heat and power plants at Duisport, the inland port of Duisburg, supplying heat and power to Germany's first carbon-neutral container terminal as part of the enerPort project. “enerPort is still a research project, but 2026 is when things get serious,” says Rudi. That is when the engines are due to go into full production and become available to all customers. And they are set to boast some pretty impressive performance figures, with the 12-cylinder engine due to produce just under one megawatt of power output – indeed it's already shown it can do this on the test stand.

The new hydrogen engines are based on the proven mtu stationary gas engines modified as follows:

• The new turbochargers developed by Rolls-Royce are larger than those used in gas engines because they have to compress greater quantities of air.  
• The cylinders have been re-designed for hydrogen use – with lower compression ratios to cater for hydrogen's fast ignition characteristics.  
• Injection system: Unlike gas engines, hydrogen is not added to the charge air until just before it enters the cylinder. The presence of hydrogen in the charge-air duct would make the risk of uncontrolled combustion too great because the fuel ignites so easily.    
• A new engine management system is used to control the complex hydrogen combustion process. This will also read pressure sensors in the cylinders, for example, which are not required in stationary gas engines.

Conversion kit for existing gas engines

Andrea, Rudi and colleagues are not just working on a new hydrogen engine, they're also developing a conversion kit for existing mtu gas engines at the same time. “This will give the customer a way to convert a gas engine into a hydrogen engine, say as part of a major overhaul,” Rudi tells us.  

This is because hydrogen engines are not yet in demand for power generation applications, as the return on investment is small. For one thing, green hydrogen – produced using energy from renewable sources – is hard to come by, and for another, it's still far too costly. That's ultimately set to change. Hydrogen projects are on the increase all over the world, and it's safe to assume the fuel will soon be available – and economical into the bargain.   “When we get to that stage, customers can use the conversion kits to convert their existing gas engines to hydrogen – or buy a gas engine today, knowing they can convert it to hydrogen at a later date,” he continued.  

Internal combustion engines – part of the mtu hydrogen ecosystem

The mtu hydrogen engines are part of a veritable hydrogen ecosystem, with Rolls-Royce engineers also working on fuel cells for stationary power supply systems. “Customers will then have a technology choice between combustion engines and fuel cells – both able to generate green power, but with different focuses,” says Andrea Prospero.  

A fuel cell is the better choice for customers requiring constant levels of electrical power, but if they also want to use the thermal energy and maybe run a district heating grid, they’re more likely to go for a hydrogen engine as part of a classic CHP set-up.  

Fuel cells and combustion engines as energy storage systems

Both fuel cells and internal combustion engines are also set to play a key role whenever energy needs to be stored. In future, more and more electricity will be generated from renewables – for example with the aid of solar panels or wind turbines. In an ideal world, this renewable electricity would be produced as and when it’s required, but the world is not always an ideal place, and wind turbines produce most power when there is a lot of wind. Likewise, solar power systems are especially effective when the sun is shining.  

Electrolyzers to produce hydrogen  

This results in lots of electricity that cannot always be used right away, meaning it has to be stored. Storage can be undertaken with the aid of battery banks, and indeed it's also possible to store electricity in the form of fuel. With this in mind, Rolls-Royce is developing electrolyzers which break water down into its constituent parts (oxygen and hydrogen) using an electrochemical process powered by electricity. The hydrogen is stored in special buffer tanks to supply electrical abd thermal power via a fuel cell or CHP plant – equipped with the new mtu hydrogen engine – when wind turbines and solar arrays are temporarily inactive.  

But until we get that far, Andrea Prospero and Rudi Hoff have to carry on tuning their engines and make sure no more 'events' happen. “We'll manage that,” say the two confidently. And the confidence and good humor they exude is contagious.