Automotive Engineer

Direct-injection systems were first developed for diesel engines more than 100 years ago, but the technology was far from durable. Fuel injected directly into the chamber often leaked. But it was a technology that many engineers saw great benefit in. One such person was Knut Jonas Elias Hesselman. 

The young engineer began his career working for AB Diesels – today known as Atlas Copco – serving as head of design among other roles. The company made engines under licence from firms in Germany, but the early powertrains were rough and problematic. Hesselman spent much of his time improving the technology, until he invented his own solution to the many problems that affected the first generation of diesel engines.

The Hesselman engine used both gasoline and diesel to improve durability and efficiency.

Originally designed for commercial vehicles, the Hesselman engine used an injection system to spray fuel into the combustion chamber. Because of the relatively low compression ratio, the engine initially fired using gasoline spark ignition, before reverting to either diesel or kerosene.

Although the engine was an unusual design, Hesselman’s focus on the injector technology, and having greater control over the amount of fuel used and injection timings, allowed it to become a commercial success and to overcome the problems of earlier systems.

In Hesselman’s 1920 patent application, he said: “In fuel-injection devices for internal combustion engines of the known kind in which fuel is injected directly, leakage in one way or another is unavoidable. It has not been possible to obtain a reliable diaphragm for this purpose, capable of withstanding the high pressure required in the fuel-supplying conduit of a modern high-pressure internal combustion engine.”

To meet this challenge, Hesselman introduced: “A combination of a plurality of pairs of annular diaphragms in which the diaphragms of each pair are connected at their inner edges by means of cylindrical walls formed integral with said diaphragms while the diaphragms of adjacent pairs are connected together by separate rings embracing said diaphragms, spacing means being provided to hold the various pairs of diaphragms at proper distance apart.”

The engine was quickly adopted by Swedish OEMs such as Scania, Volvo and Tidaholms Bruk, but it wasn’t free from problems.

Owing to the low compression ratio it was difficult to reach the correct working temperature, resulting in incomplete combustion, which fouled the spark plugs. This meant that exhaust emissions, even for the early part of the 20th century, were unacceptable. Because of this, the OEMs that had adopted Hesselman’s engine reverted back to traditional diesel powertrains.

But his technology proved the efficiency of gasoline direct injection. And although Hesselman’s design was not a unanimous success it led the way for other manufacturers to introduce the technology. 

The 1952 two-seater Gutbrod Superior, which used a 663cc two-cylinder engine, was the first car to use the technology. But it was the Mercedes-Benz 300SL in 1955 that brought the system to the public eye.

The Bosch system placed the fuel injectors into the bores on the cylinder wall used by the spark plugs in the six-cylinder engine. The system helped to double the power of the engine.

Since its inclusion, gasoline direct injection has been used to improve performance and efficiency.

Hesselman’s original design was engineered to boost durability, but the legacy of his work is improving the combustion process and reducing emissions.