Toyota filed a patent last month for a hydrogen-powered gas turbine combustor. It’s a compact spinner designed to produce between 13 and 130 horsepower, but to what use? And is it feasible or just a quirky engineering idea?
Back to the sixties
As a strong – and increasingly isolated – believer in hydrogen for passenger car propulsion, Toyota’s turbine is, admittedly, a piece of elegant engineering. It’s also a solution that dates back to the sixties.
In 1963, Chrysler’s Turbine Car could run on tequila, spin to 36,000 rpm, and looked like a crossover between a plane and a car. Interestingly, the company built fifty of them. But the technology never took off because turbines, once you shrink them for passenger cars, drink too much fuel and exhale heat at uncomfortable levels.
A turbine can run on different fuels, but Toyota thinks hydrogen changes the equation. This is actually Toyota’s third hydrogen interpretation. The company already builds fuel-cell sedans and also uses them in internal combustion. The strongest advocate of the former is the Mirai; the Corolla Cross H2 Concept showcased the latter three years ago. Toyota said it was 40% of the way to commercialization, but three years later, hydrogen ICE remains a motorsport curiosity.
Scale is the problem
Now comes the turbine. The patent describes a gas turbine combustor, the chamber where air and fuel meet and burn. In a conventional gas turbine, compressed air enters a can-like chamber, fuel sprays in, igniters fire, and the expanding gases spin a turbine wheel. That wheel drives a compressor and, hopefully, leaves enough surplus power to turn a driveshaft or generator.
Toyota’s problem is scale. A naval turbine makes thousands of horsepower. Toyota wants between 13 and 130. That is moped-to-motorcycle territory. At that size, the combustor becomes thermal chaos. The patent admits it needs a “less complex structure”, which is engineering code for “we are trying to stop this thing from spinning out of control”.
Uniform combustion
Then there’s the fuel. Hydrogen is lighter than gasoline or kerosene, and it burns much hotter. That is great for power density. It is terrible for everything else. In a standard combustor, you spray fuel, ignite it, and hope the mixture lights uniformly. With hydrogen, that does not work. The fuel disperses differently, and nitrogen oxides are generated at levels that would make a diesel engineer blush.
Toyota’s solution is a cluster of small fuel injectors arranged through the combustor. Each injector receives compressed air and hydrogen through two separate passages. The two streams meet inside the nozzle, mix thoroughly, and then an igniter built into the injector fires.
The result is not one big flame but many smaller, distributed ones. That uniformity is important because it prevents pockets where too much hydrogen meets too little air. It also means the flames reach corners of the combustor that a single central injector would leave cold. That would result in lost power and efficiency.
Heat losses
Gas turbines are thermodynamically efficient at large scale and high temperature. If you shrink them, they suffer. Heat losses become a larger percentage of total energy. The rotational inertia that makes a turbine smooth in airplanes becomes a nightmare in stop-and-go traffic. Chrysler proved this in 1963. Its turbine car idled at exhaust temperatures that could melt the bumper of the car behind it.
Hydrogen does not fix that. It changes the chemistry inside the combustor, but the turbine wheel still needs to extract work from hot gas. The multi-injector approach is genuinely interesting engineering. But the turbine itself is a solution for a problem that batteries have already solved with fewer parts. And without exotic fuel on an existing grid.
It is difficult to see how this could be put into practice. Other than a generator function in an EREV setup, the turbine doesn’t seem to be the best bit for forcing a hydrogen breakthrough in passenger car mobility.
