PAD 8D6544 - Caterpillar

To ensure precise regulation of fuel flow, carburetors are not used. Fuel flow is controlled with a fuel metering valve in order to maintain precise control of fuel delivery to the engine. Illustration 1 is a schematic of the fuel system.
Illustration 1 g03793820Gas from the main gas supply flows through a gas pressure regulator. Gas pressure to the regulator must be 483 to 1724 kPa (70 to 250 psi). Lower pressure may result in reduced power. Pressure from the regulator to the engine must be 448 34 kPa (65 5 psi). The fuel pressure must be stable to 1.7 kPa ( .25 psi).The gas flows through a gas shutoff valve into the fuel metering valve. The ECM issues a command signal to a fuel metering valve in order to control the flow of fuel to the fuel manifold. The signal is based on the difference between the actual engine rpm and the desired engine rpm.The flow of gas from the fuel manifold is divided. There is a gas line for each cylinder. Most of the gas flows through the gas line, an orifice, and a gas admission valve to the inlet port for the cylinder. The inlet air that is necessary for combustion also flows into the inlet port. The gas and combustion air flow through the inlet port and the openings for the inlet valves to the cylinder's main combustion chamber.Each cylinder has a smaller gas line. The remainder of the gas flows through the smaller gas line. The gas is regulated by an adjustable needle valve before the gas flows into the precombustion chamber.The rich air/fuel mixture in the precombustion chamber is ignited by the spark plug. This action ignites the leaner air/fuel mixture in the main combustion chamber. Exhaust exits the cylinder through the openings for the exhaust valves.Precombustion Chamber and Main Combustion Chamber
Illustration 2 g03793879
(1) Fuel inlet passage
(2) Check valve
(3) Passages for the engine coolant
(4) Precombustion chamber The gas supply flows through a small line from the fuel manifold through an adjustable needle valve. Adjustment of the needle valve helps to provide the desired combustion burn time.The gas flows through fuel inlet passage (1) into check valve (2) at the top of precombustion chamber (4). A ball at the bottom of the check valve moves away from the orifice during the intake stroke in order to admit gas into the precombustion chamber.The gas in the precombustion chamber is mixed with some combustion air from the main combustion chamber. The rich air/fuel mixture in the precombustion chamber is ignited by the spark plug. The ball at the bottom of the check valve is forced upward by compression from combustion in order to stop the flow of gas through the check valve.Coolant flows through passages (3) in order to cool the precombustion chamber.
Illustration 3 g03793872
(2) Check valve
(4) Precombustion chamber
(5) Gas admission valve
(6) Combustion air
(7) Main combustion chamber The flow of combustion air (6) into the cylinder head is regulated by the exhaust bypass (wastegate) and the