The precombustion chamber was first used on the Hornsby-Ackroyd lowcompression oil engine and subsequently by Caterpillar, Deutz, and Mercedes-Benz, and other diesel manufacturers (Fig. 7-2). The precombustion chamber, also known as a hot bulb because of its shape and absence of any provision for cooling, occupies 25–40% of the total swept volume.
As the piston approaches tdc, the injector opens to send a solid stream of fuel into the hot bulb. The charge ignites, bulb pressure rises, and a stream of burning fuel jets through the connecting channel and into the main chamber, where there is sufficient air to complete combustion. The smaller the channel, the greater the acceleration and, all things equal, the more complete the fuel-air mixing. These chambers employ pintle-type injectors.