The hot-bulb engine is a type of internal combustion engine in which fuel ignites by coming in contact with a red-hot metal surface inside a bulb, followed by the introduction of air (oxygen) compressed into the hot-bulb chamber by the rising piston. There is some ignition when the fuel is introduced, but it quickly uses up the available oxygen in the bulb. Vigorous ignition takes place only when sufficient oxygen is supplied to the hot-bulb chamber on the compression stroke of the engine. Most hot-bulb engines were produced as one or two-cylinder, low-speed two-stroke crankcase scavenged units. History Four-stroke Hornsby-Akroyd oil engine The concept of this engine was established by Herbert Akroyd Stuart, an English inventor. The first prototypes were built in 1886 and production started in 1891 by Richard Hornsby & Sons of Grantham, Lincolnshire, England under the title Hornsby Akroyd Patent Oil Engine under licence. Two-stroke hot-bulb engines Some years later, Akroyd-Stuart's design was further developed in the United States by the German emigrants Mietz and Weiss, who combined the hot-bulb engine with the two-stroke scavenging principle, developed by Joseph Day to provide nearly twice the power, as compared to a four-stroke engine of the same size. Similar engines, for agricultural and marine use, were built by J. V. Svensons Motorfabrik, Bolinders, Lysekils Mekaniska Verkstad, AB Pythagoras and many other factories in Sweden. Comparison to a diesel engine Akroyd-Stuart's engine was the first internal combustion engine to use a pressurised fuel injection system and also the first using a separate vapourising combustion chamber. It is the forerunner of all hot-bulb engines, which is considered the predecessor to diesel engines with antechamber injection. The Hornsby-Akroyd oil engine and other hot-bulb engines are different from Rudolf Diesel's design, where ignition occurs through the heat of compression alone: An akroyd engine will have a compression ratio between 3:1 and 5:1, whereas a typical diesel engine will have a much higher compression ratio usually between 15:1 and 20:1, making it more efficient. Also, in an akroyd engine the fuel is injected during the early intake stroke (at 140° BTDC) and not at the peak of compression (at 15° BTDC) as in a diesel engine. Operation and working cycle The hot-bulb engine shares its basic layout with nearly all other internal combustion engines, in that it has a piston, inside a cylinder, connected to a flywheel by a connecting rod and crankshaft. Akroyd-Stuart's