Hydrogen will play an increasingly important role in the push toward greater use of renewable energy and the reduction in carbon emissions from the transportation sector, electrical energy generation and transmission, and the production of commodity chemicals, such as ammonia and polyolefins. In this chapter, the operating principles of fuel cells and electrolyzers are detailed. The main function of these devices is the interconversion of electrical and chemical energy.

Gas turbines play a preeminent role in the stationary power generation marketplace and are expected to remain a critical part of the market mix for the foreseeable future. Alternative technologies compete with gas turbines in certain size classes, but at power generation levels above 5 MW, gas turbines offer the most attractive option due to their relatively low capital, operating, and maintenance costs. The configurations for these systems involve high efficiencies as well. These engines are being looked to by the US Department of Energy and the major OEMs for clean power production, especially considering the use of renewable fuels. As a result, the market will continue to demand gas turbines for the foreseeable future.

Gas turbines are able to utilize a wide variety of fuels, including fuels with low- or zero-carbon content. This includes hydrogen (H2), ammonia (NH3), synthetic and renewable natural gas, as well as a range of biofuels. These are sometimes referred to as zero-carbon, net-zero-carbon, or near-zero-carbon fuels. A subset of these fuels have been used to produce power from gas turbines for decades. This chapter will review experience and practical challenges in the use of these fuels in gas turbines for power generation applications, describing case studies for utilizing these fuels in the field.

Reciprocating internal combustion engines rely on a piston-cylinder configuration to achieve a batch periodic conversion from chemical energy in a fuel to mechanical energy leaving an engine. In this category of energy conversion devices are included spark-ignition (SI) engines which may operate on gaseous or liquid fuels, and compression-ignition (CI) engines which may operate on liquid or a combination of liquid and gaseous fuels. As described by Lichty, the first example of an internal combustion engine was that of Abbé Hautefueille in 1678 using the combustion of gunpowder in a cylinder to move a piston and produce work. Renewable fuels and bio-based chemicals and materials are nothing new. They have served humankind since the dawn of civilization. And that there would be changes in how we power our transportation systems is also nothing new.

Liquid hydrocarbon fuels are an essential component of our energy system.  They have unprecedented volumetric density of energy, roughly 32 MJ/liter for gasoline, compared to a lithium ion battery at 2.4 MJ/liter.  This means that for activities requiring high or sustained power delivery such as flying and shipping there are no current alternatives.  Compared to electric motors, internal combustion engines have significantly lower efficiency, and the recent improvements in the electric vehicle sector suggest that at least for light vehicle duty their use is not essential.  However, despite significant government action to promote electrification of the light duty fleet, there will still be a period of transition that could last well over a decade as the developing world increases its consumption of transportation services and the world builds the capacity to electrify personal transportation.  Therefore, there is an urgent need to develop pathways to produce renewable liquid hydrocarbon fuels as part of the energy transition to low carbon energy systems.

Gas turbine engines for aircraft applications are complex machines requiring advanced technology drawing from the disciplines of fluid mechanics, heat transfer, combustion, materials science, mechanical design, and manufacturing engineering. In the very early days of gas turbines, the combustor module was frequently the most challenging. Although the capability of the industry to design combustors has greatly improved, challenges still remain in the design of the combustor, and further innovations are required to reduce carbon emissions. Many companies in the aviation industry committed to a pathway to carbon-neutral growth and aspire to carbon-free future in 2008. Additionally, airframers have aggressive goals to reduce carbon dioxide emissions by 50% by 2050 compared to those in 2005. Achieving these goals require technology advancements in all aspects of the aviation industry including airframers, engine manufactures fuel providers, and all the associated supply chains. The focus of this chapter is the influence of one module of the aircraft engine – the combustor.

Gas turbines play a preeminent role in the stationary power generation marketplace and are expected to remain a critical part of the market mix for the foreseeable future. Alternative technologies compete with gas turbines in certain size classes, but at power generation levels above 5 MW, gas turbines offer the most attractive option due to their relatively low capital, operating, and maintenance costs. The configurations for these systems involve high efficiencies as well. These engines are being looked to by the US Department of Energy and the major OEMs for clean power production, especially considering the use of renewable fuels. As a result, the market will continue to demand gas turbines for the foreseeable future.

The global push for economy-wide decarbonization is fueling intense interest in the potential of hydrogen as a zero-carbon resource. Long coveted as a fuel of the future, hydrogen already is being used in a variety of applications to cut carbon emissions across the globe. This chapter details a case study from Mitsubishi Power in use of hydrogen in gas turbines to produce electricity. Currently, Mitsubishi Power’s largest and most advanced gas turbines make use of a dry low-NOx (DLN) combustion system that allows operation with up to 30% hydrogen in baseline configuration. Going forward, increasing the use of hydrogen as a percentage of a power station’s fuel mix – from a mixture of around 30% hydrogen all the way up to 100% hydrogen as an energy source – requires the need for innovative equipment modifications, such as a multi-cluster combustor.

Gaseous renewable fuel combustion is of primary interest for a range of applications including aircraft engines, ground power engines, reciprocating engines, and industrial furnaces, among others. While much of the combustion science and engineering that are needed to design and operate such devices is well developed and available in modern textbooks, the attainment of even higher efficiencies, greater performance, and reduced emissions for an ever-increasing array of new fuels and fuel blends requires an even deeper understanding of fundamental combustion concepts and the underlying physical and chemical phenomena. In many cases, these fundamental concepts are areas of much recent and ongoing research.  This chapter describes the basic combustion and chemical kinetic properties of the fuels, namely hydrogen, syngas, ammonia, methane, natural gas, and ethanol, considering the flame temperature, ignition delay time, flammability limit, laminar flame speed, and fuel stretch sensitivity.

Nearly one-third of the energy produced in the US comes from liquid fuels derived from crude oils, natural gas plant liquids, and other condensates. Fuel atomization to produce spray(s) is necessary for practical combustion systems employing liquid fuels. This requirement stems directly from the high energy density of the liquid fuels. Despite the major changes underway in the portfolio of liquid fuels, fuel atomization and combustion systems have remained vastly unchanged. The current practice is to design drop-in liquid biofuels that can be used “as is” in existing combustion devices. However, such fuels can be energy intensive to produce and create wasteful byproducts, eroding the carbon footprint benefits of the liquid biofuels. Thus, it is imperative that the liquid fuel injection, atomization, and combustion systems of the future consider increased fuel flexibility to utilize both fossil and alternative fuels from multiple sources within the same combustor hardware. Fuel properties and fuel atomization and combustion hardware should be co-optimized to minimize the carbon footprint based on the life-cycle analysis of the fuel. This chapter discusses atomization of renewable liquid fuels, detailing the phenomenology and controlling physical processes.

A major motivation for the development and ultimate replacement of petroleum-based fuels with alternatives is the desire to reduce the carbon emissions (i.e., CO2) created when burning hydrocarbon fuels in prime mover devices. In addition to CO2, combustion of hydrocarbon fuels in air will inevitably create a number of other emissions (e.g., NOx, soot, etc.), which can have detrimental effects on human health or the local (or global) environment. Furthermore, the desire for a more economic and stable fuel supply has also provided impetus for the identification of alternative feedstocks for fuels. With these motivations to find alternative fuels for power generation, it is important to understand how different fuels can impact pollutant formation. This chapter focuses on the fundamentals of pollutant formation in combustion, as well as the impact of various alternative fuels on the combustion generated emissions. This includes carbon monoxide, nitrogen oxides (NOx), and soot. These topics are addressed for a variety of candidate fuels, including hydrogen and ammonia.

Liquid hydrocarbon fuels are an essential component of our energy system.  They have unprecedented volumetric density of energy, roughly 32 MJ/liter for gasoline, compared to a lithium ion battery at 2.4 MJ/liter.  This means that for activities requiring high or sustained power delivery such as flying and shipping there are no current alternatives.  Compared to electric motors, internal combustion engines have significantly lower efficiency, and the recent improvements in the electric vehicle sector suggest that at least for light vehicle duty their use is not essential.  However, despite significant government action to promote electrification of the light duty fleet, there will still be a period of transition that could last well over a decade as the developing world increases its consumption of transportation services and the world builds the capacity to electrify personal transportation.  Therefore, there is an urgent need to develop pathways to produce renewable liquid hydrocarbon fuels as part of the energy transition to low carbon energy systems.