You are looking for a new car (about 100 kW nominal power) with the best possible energy efficiency. Which of the engine options should you choose solely based on the engine efficiency?Image: Wikimedia commons, CC BY-SA 4.0.

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BlackTom AI · Accepted Answer

Question restatement: You are looking for a new car (about 100 kW nominal power) with the best possible energy efficiency. Which of the engine options should you choose solely based on the engine efficiency?

Option a: Gas turbine. Gas turbines in automotive use tend to have relatively high power-to-weight and fast response, but their thermal efficiency is typically not as high as modern fuel cell systems when evaluated in a comparable automotive cycle. They also suffer from high fuel consumption at part load and require complex accessories, which reduces overall energy efficiency in a passenger car context. In short, when judging engine efficiency in a car, a gas turbine generally does not outperform a fuel-cell system.

Option b: Gas engine. A conventional internal combustion engine (gasoline or diesel) achieves decent performance, but its peak cycle efficiency is limited by combustion chemistry, friction, heat losses, and throttling. Real-world automotive gas engines often operate with overall efficiency significantly lower than that of fuel cells, especially when considering the entire drivetrain. This makes them less energy-efficient than fuel cells for the same peak power rating.

Option c: Fuel cell. A fuel cell converts stored chemical energy directly into electrical energy with relatively high efficiency, particularly when considering the electric drivetrain and regenerative aspects of modern vehicles. When evaluating engine efficiency alone, fuel cells typically provide higher electrical efficiency than internal combustion engines or gas turbines, leading to lower fuel consumption for the same customer-perceived performance in a car of this power class. The account of losses (air operations, cooling, parasitic loads) is often more favorable for fuel cells in this comparison, which is why fuel cells are commonly cited as the most energy-efficient option among the three presented in this context.

Additional considerations: While this question focuses on engine efficiency in isolation, real-world choice also depends on fuel type, fueling infrastructure, cost, maintenance, and system integration. The analysis here isolates efficiency to compare the intrinsic conversion efficiency of each option, not the total life-cycle or user experience. In other words, fuel cells tend to have the best intrinsic efficiency among the three options for a ~100 kW power level, when judged purely on how effectively each option converts chemical energy to usable electrical energy for propulsion.

Climate Action - PtX X-to-power

You are looking for a new car (about 100 kW nominal power) with the best possible energy efficiency. Which of the engine options should you choose solely based on the engine efficiency?Image: Wikimedia commons, CC BY-SA 4.0.

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You are looking for a new car (about 100 kW nominal power) with the best possible energy efficiency. Which of the engine options should you choose solely based on the engine efficiency?Image: Wikimedia commons, CC BY-SA 4.0.

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