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How a Hot Bulb Engine Works

        Auto | Types of Engines

Becoming a Part of History
A 2-cylinder, 70 horsepower hot bulb engine built by W.H. Allen & Sons in 1923. The engine is on display at the Internal Fire Museum of Power, Tangygroes, Wales, UK.
A 2-cylinder, 70 horsepower hot bulb engine built by W.H. Allen & Sons in 1923. The engine is on display at the Internal Fire Museum of Power, Tangygroes, Wales, UK.
Photo courtesy of J.Grover

By the early 20th century most of the problems with machining efficient and strong gas and diesel engines were worked out. Engineers also solved the problems associated with spark ignition, compression ignition, timing and governing of engine speed and power. There was also a growing accessibility to more refined, and therefore more efficient, fuel. All these factors led to the slow death of the hot bulb engines.

Consider the power behind a hot bulb engine. Though they were built large enough to generate 60 horsepower their compression ratio remained small, about 5 to 1. Even a crude diesel engine could generate a compression ration of about 15 to 1. This meant more power and more torque, all in a smaller, more convenient package.

Hot bulb engines were used in Scandinavia until the 1930s, and are still seen, albeit rarely, in canal boats in England. However, for the most part, hot bulb engines are now more curiosities rather than useful tools.

"It was a great source for its time and place," Foster said, adding hot bulb engines simply couldn't keep pace with changes in technology. "I think you could say it was the missing link between the first engines and modern engines," he said.


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