Hot Bulb Engine - Compression Ignition

Compression Ignition

Herbert Akroyd Stuart was always keen to improve the efficiency of his engine. The obvious way to do this was to raise the compression ratio to increase the engine's thermal efficiency. However, above ratios of around 8:1 the fuel oil in the vapouriser would ignite before the piston reached the limit of its travel. This pre-detonation caused rough running, power loss and ultimately engine damage (see engine knocking for more information). Working with engineers at Hornsby's, Akroyd Stuart developed a system whereby the compression ratio was increased to as much as 18:1 and fuel oil was delivered to the cylinder only when the piston reached top dead centre, thus preventing pre-ignition.

This system was patented in October 1890 and development continued. In 1892 (5 years before Rudolf Diesel's first prototype), engineers at Hornsby's built an experimental engine. The vapouriser was replaced with a standard cylinder head and used a high-pressure fuel nozzle system. The engine could be started from cold and ran for 6 hours, making it the world's first internal combustion engine to run on purely compression ignition. However, to build a fully practical fuel injection system required using machining techniques and building to tolerances that were not possible to mass produce at the time. Hornsby's was also working at full capacity building and selling hot-bulb engines, so these developments were not pursued.