and Bournville II in 1911—were powered by 15 horsepower Bolinder single-cylinder hot bulb engines, and this type became common between the 1920s and the 1950s. With hot bulb engines being generally long-lived and ideally suited to such a use, it is not uncommon to find vessels still fitted with their original hot bulb engines today. Although there is a common misconception that model glow plug engines are a variation of the hot bulb engine, this is not the case. Model glow engines are catalytic ignition engines. They take advantage of a reaction between platinum in the glow plug coil and methyl alcohol vapour whereby at certain temperatures and pressures platinum will glow in contact with the vapour. Hot bulb pseudo-diesel development 1890s–1910 The hot bulb engine is often confused with the diesel engine, and it is true that the two engines are very similar. A hot bulb engine features a prominent hot bulb vaporiser; a diesel engine does not. Other significant differences are: The hot bulb engine mostly reuses the heat retained in the vaporiser to ignite the fuel, achieving about 12% efficiency. The diesel engine uses only compression to ignite the fuel. It operates at pressures many times higher than the hot bulb engine, resulting in over 50% efficiency with large diesels. The hot bulb engine requires preheating of the hot bulb, often with a torch, for about 15 minutes before starting. There is also a crucial difference in the timing of the fuel injection process: In the hot bulb engine, before 1910 fuel was injected earlier into the vaporiser (during the intake stroke). This causes the start of combustion to be out of synchronization with the crank angle, meaning that the engine would only run smoothly at one low-speed or load. If the engine's load increased, so would the temperature of the bulb, causing the ignition period to advance, causing pre-ignition. To counteract pre-ignition, water would be dripped into the air intake, providing some flexibility. In the diesel engine, fuel is injected into the cylinder, with an adjusted timing relative to the engine speed and load, shortly before the top dead center of the compression stroke is reached. There is another, detailed difference in the method of fuel injection: The hot bulb engine uses a medium-pressure pump to deliver fuel to the cylinder, through a simple nozzle. In the original diesel engine, fuel was sprayed into the cylinder