Heading for hydrogen: solutions from Kistler for more sustainable combustion engines

With efforts under way to achieve decarbonization in the next few decades, hydrogen has an important part to play: production will make increasing use of renewable energies, so this gas is becoming more and more attractive as a clean energy source. The Kistler Group is making a decisive contribution to this transformation by providing technologies to monitor and control the highly reactive combustion of hydrogen.

The important role that hydrogen has to play was recognized long ago: "Water is the coal of the future!" When Jules Verne wrote these words in 1874, he was envisioning advances in electrolysis, the process that allows water to be split into its components – hydrogen and oxygen. What is known as the "hydrogen economy" was described in detail for the first time as an alternative to fossil fuels in the 1970s and 1980s. In reality, however, a number of obstacles stand in the way of implementing such a project. On the one hand, there are the specific properties of the lightest element such as reactivity, volatility, low energy density measured by volume, and a very low liquefaction temperature – to name but a few. Above all, the lack of a suitable infrastructure – which means that high initial investments are needed – has repeatedly put the brakes on the development of hydrogen, despite the hopes that it holds out. But now, hydrogen's time finally seems to have arrived.

This change has been brought about by political initiatives and programs that offer economic incentives to open the way for investments in technologies and infrastructure. In 2017, Japan became the first country in the world to launch a hydrogen strategy. Since then, many more countries have followed suit – including the EU and Germany in 2020. Hydrogen only occurs on earth in bound form, so it has to be produced before it can be used: the critical issue, therefore, is large-scale production. By 2024, one million tonnes of "green hydrogen" are due to be produced with renewable energies in the EU – and by 2030, the figure is already set to rise to ten million. The Power-to-X (PtX) approach holds out great promise in this context: the surplus of renewable energies (photovoltaics, wind power) resulting from natural fluctuations is used, for example, to produce hydrogen that can be stored temporarily and utilized as a clean energy source for vehicles, aircraft and power plants as needed.

Highly promising investments and programs

Since the required amounts of hydrogen will not suddenly become available overnight, there is a need for bridging technologies that can operate with variable hydrogen components and different energy sources. Large engines and marine engines are good examples of this. For instance, the world's largest shipping company aims to move away from climate-damaging heavy oil and diesel by switching to alternative, synthetically produced fuels such as methanol, ethanol or ammonia (power-to-fuel) – with the goal of becoming fully climate-neutral by 2050. To meet these demands, marine engine manufacturers are called upon to make their propulsion units more versatile (multi-fuel) – and also to offer the option of retrofitting variable technology. Approaches with over ten different fuels are already available.

By providing precise, robust cylinder pressure sensor technology as part of closed loop combustion control, Kistler is already helping to cut fuel consumption by marine engines and make them more fuel-flexible – with reductions in carbon dioxide emissions of up to two percent, equivalent to 200 tonnes of CO2 per year and engine, depending on engine power. Savings due to optimized combustion will have even more of an impact in the case of new, potentially synthetic fuels, because these will be more cost-intensive at first. This has prompted Kistler to collaborate with customers on testing the suitability of cylinder pressure sensors for hydrogen drive systems and fuels that contain hydrogen. One effect of hydrogen that requires attention is what is known as embrittlement: the light and highly volatile molecules penetrate metal surfaces, where they can lead to a sort of accelerated corrosion – and given the long lifetimes of marine engines, this is an additional challenge that has to be overcome.

A key element in sustainable combustion

A second challenge is presented by the highly reactive combustion of hydrogen – the higher the hydrogen component, the faster and hotter the flame will burn. This phenomenon is especially evident in the application area of gas turbines. Here too, companies in many industrialized countries have committed to decarbonization by 2050 by gradually increasing the proportion of hydrogen in the gas used to 100 percent. Manufacturers are already offering units with dual- and multi-fuel capability that can burn fuels with hydrogen content of up to 20 percent. Measurement instrumentation in the combustor was often used in the past as a way of reducing emissions – but with higher hydrogen percentages, this is becoming a fundamental prerequisite for safe and reliable operation.

With the help of high-temperature-pressure sensors from Kistler that can be positioned close to the flame, it is already possible to operate gas turbines with 50 percent hydrogen and – after conversion – even 100 percent hydrogen should be possible in the future. These sensors are extremely temperature-stable – they can withstand 700°C in continuous operation and even 1,000°C for short periods. Their measurement data can be used not only in development work but also for real-time monitoring of the gas turbine during actual operation. This is particularly important in order to prevent what are known as flashbacks – the premature onset of combustion that can cause irreparable damage to components.

What is the path to clean aviation?

The increase in the hydrogen component that was developed for gas turbines can also be applied to aircraft engines on the basis of the same technological principle. This application is already operating in the laboratory with sensors from Kistler, but there are still some obstacles to practical implementation. Apart from the safety aspect, it would require a large volume of hydrogen, leading to modification or reduction of the size of the passenger cabin – and this would tend to make the solution more uneconomical at first. The use of liquid hydrogen has emerged as a highly promising approach that is being pursued by at least one major manufacturer. Experiments are also under way with synthetic fuels that allow largely CO2 -neutral operation of aircraft engines. However, we must wait and see how far these new approaches can break through the feasibility threshold and become cost-effective on a large scale.

As an expert in optimizing combustion technologies, the Kistler Group provides its customers with the means to successfully accomplish the journey towards decarbonization. The focus is not only on continuously improving available technologies, but also on the approaches described here to hydrogen-based aviation, heat and energy production. Kistler is working in close collaboration with its customers to continue developing the technologies needed to achieve these goals, including cylinder pressure sensors, high-temperature pressure sensors and accelerometers as well as monitoring and control systems.

 

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