Combustion Chamber Configuration

The shape and depth of the combustion chamber and piston, the number and placement of valves, the design of intake ports (designed for greater swirl), and the placement of the injectors all play a role in clean diesel design and reduction of particulate matter and nitrogen oxides. Also important to clean diesel combustion chamber configuration are the two methods of supplying pressurized fuel: direct and indirect fuel injection. Remember that indirect injection means the fuel is injected into a separate chamber in the cylinder head, often called a prechamber Figure 54-10, and direct injection means the fuel is injected directly into the combustion chamber Figure 54-11.

FIGURE 54-10
With indirect injection, fuel is injected into a separate combustion chamber.
FIGURE 54-11
With direct injection, the fuel is injected directly into the combustion chamber.

Older diesel engines typically used the direct injection system. Since it injected the fuel directly into the cylinder, it was a simple and powerful design. Unfortunately, it produced excessive smoke and high exhaust emissions. A better design was the indirect injection system that used a separate chamber, or combustion area, to better control emissions and the noise level of the engine. Often called a prechamber or precombustion chamber engine, the separate combustion chamber also provided a convenient location for glow plug installation to assist starting the engine in cold temperatures. However, with the coming of very strict emission control standards, there has been a shift back to the direct fuel injection system with electronic controls. Additionally, the latest electronically controlled fuel injection systems operate at very high injection pressures, in the range of 18,000 to 24,000 pounds per square inch (psi), or 124,000 to 165,000 kilopascals (kPa). Electronically controlling this high pressure to an infinite degree makes today’s clean diesel engine technology possible.

Diesel fuel sprayed onto hot components can cause fires. Take appropriate measures to solve any fuel or oil leaks immediately.