THERE has, for many years, been a demand for an automotive engine more economical in operation than the gasoline engine. As the Diesel engine had early established a good reputation for economy, the development work on a more economical automotive engine quite naturally centered around this type of engine.
Additional advantages can, however, be gained by combining fuel injection with spark ignition, and an engine of this type has been developed by K. J. E. Hesselman of Stockholm, Sweden. This engine is generally called the Hesselman engine.
In the spark-ignition fuel-injection engine the charge is formed at a certain time before the spark occurs, and this makes it possible to mix fuel and air thoroughly whereby high output is secured. Engines operating on fuel oil with a compression ratio of 7.5 : 1 have given a brake mean effective pressure of over 125 lb. per. sq. in.
The fuel is not injected until at the end of the compression stroke, and thus is not unduly heated by the heat of compression. A higher compression-ratio can therefore be employed in this engine than in the carburetor engine without pre-ignition or detonation. The engine thus works in an efficient cycle.