80 Diesel Engine Technology Copyright Goodheart-Willcox Co., Inc. Swirl Chamber Swirl chamber systems use an auxiliary combustion chamber known as a swirl chamber. This ball- or disk- shaped chamber has a throat area that opens at an angle to the main combustion chamber, Figure 4-38C. Unlike a standard precombustion chamber, swirl chamber volume is usually 50%–70% of top dead center cylinder volume. The swirl chamber is connected at a right angle to the main combustion chamber. A strong air vortex (mass of swirling air) is generated during the compression stroke. The injector nozzle is positioned so the injected fuel penetrates the swirling air perpendicular to its axis and strikes the opposing chamber side in a hot wall zone. As combustion begins, the air-fuel mixture is forced into the main combus- tion chamber through the throat area and mixed with the residual combustion air. The design of the swirl chamber, the arrangement and form of the nozzle jet, and the posi- tion of the glow plug (if used) must be carefully matched to ensure proper mixture at all speeds and load conditions. Energy Cells Energy cells are generally used with pintle-type injec- tion nozzles. As shown in Figure 4-39, the system contains a main combustion chamber, flat-top piston, small energy cell, and a passageway connecting the main combustion chamber to the energy cell. The energy cell is actually two separate chambers and a small passageway. The entire energy cell is shaped somewhat like a figure eight. As injection occurs, a portion of the main fuel stream crosses the main combustion chamber and enters the energy cell. The atomized portion of the fuel stream begins to burn in the main combustion chamber and the energy cell. As fuel burns in the energy cell chambers, the size and shape of the chambers force the air-fuel mixture back into the main combustion chamber at a very high speed. This creates swirl and turbulence in the main chamber. The movement of fuel and air from the energy cell to the main combustion chamber occurs at a steady rate, so combustion and engine operation are smooth and fuel economy is excellent. Diesel Fuel Injection Systems The fuel injection system is the heart of the diesel engine. Rudolf Diesel struggled with the problem of fuel injection, finally resorting to a clumsy compressed air system to blow fuel into the combustion chamber. The development of the first reliable injectors and pumps by Robert Bosch in the 1920s led to the production of modern high-speed diesel engines. Injection System Functions All diesel fuel injection systems must be designed to provide exactly the same amount of fuel to each cylinder. This ensures that the power pulses generated in each cyl- inder will be equal and that the engine will operate smoothly. The system must also be capable of generating sufficient fuel pressure at the injector nozzles. This injec- tion pressure has increased greatly with technology and some modern diesel injection systems are capable of developing pressures in excess of 40,000 psi (275,790 kPa) to force fuel into the combustion chamber. Fuel injection must be timed precisely. If fuel is injected at the wrong time, the engine will lose power. If fuel injection occurs early, the combustion chamber tem- perature will be lower than ideal and ignition will be delayed, resulting in incomplete combustion. If the ignition occurs late (after the piston has passed top dead center), the burning fuel will have more room to expand and some of the potential power in the expanding gases will be lost. The injection of the fuel must begin abruptly, continue for a specific length of time, and end abruptly. If the fuel is injected too fast, it will have the same effect as fuel that is injected too early. If fuel injection occurs slowly, it will have the same effect as fuel that is injected too late. The fuel must be atomized when it is injected into the combustion chamber. Atomization distributes the fuel throughout the air charge, increasing the surface area of the fuel exposed to the oxygen in the air. This ensures a complete burning of the air and fuel, which maximizes power output. Atomization occurs as fuel is forced out of the openings in the fuel injector tip. The design of the com- bustion chamber and the piston head also helps to mix the air and fuel together. A governor is needed to regulate the amount of fuel fed to the cylinders. The governor ensures that there is suf- ficient fuel delivered at idle to prevent the engine from stalling. It also cuts the fuel supply when the engine reaches its maximum rated speed. Without a governor, a diesel engine could quickly reach speeds that would destroy it. The governor is often included in the design of the fuel injection pump. Cell clamp Cell cap Injection nozzle Cell body Locating pin Cell clamp screw Figure 4-39. Typical energy cell combustion chamber. This design is actually two separate chambers and creates great turbulence which helps the air-fuel mixture to better mix for good combustion.