After studying Chapter 4, the reader should be able to:

2. After studying Chapter 4, the reader should be able to: • Prepare for Engine Repair (A1) ASE certification test content area “E” (Fuel, Electrical, Ignition, and Exhaust System Inspection and Service). • Explain how a diesel engine works. • Describe the difference between direct injection (DI) and indirect injection (IDI) diesel engines. • List the differences between mechanical fuel injection and common rail (electronic) fuel injection. • List the parts of the typical diesel engine fuel system. • Explain how glow plugs work. • List the advantages and disadvantages of a diesel engine.

3. DIESEL ENGINES • In 1892, a German engineer named Rudolf Diesel perfected the compression-ignition engine that bears his name. • The diesel engine uses heat created by compression to ignite the fuel, so it requires no spark ignition system.

4. DIESEL ENGINES • The diesel engine requires compression ratios of 16:1 and higher. • Incoming air is compressed until its temperature reaches about 1,000°F (540°C). • This is called heat of compression. • As the piston reaches the top of its compression stroke, fuel is injected into the cylinder, where it is ignited by the hot air. See Figure 4-1 (next)

5. DIESEL ENGINES Figure 4 - 1

6. DIESEL ENGINES • A diesel engine uses individual fuel injectors. • On injector-pump-type fuel systems a precision injection pump delivers fuel to the injectors. • Each injector delivers the fuel exactly, spraying it into the combustion chamber at the precise moment required for efficient combustion. See Figure 4-2 and 4-9 (next)

7. DIESEL ENGINES Figure 4 - 2. A typical injector-pump-type diesel fuel system

8. DIESEL ENGINES • In a diesel engine, air is not controlled by a throttle as in a gasoline engine. • Instead, the amount of fuel injected is varied to control power and speed. • This higher air-fuel ratio and the increased compression pressures make the diesel more fuel-efficient than a gasoline engine in part because diesel engines do not suffer from throttling losses.

9. DIESEL ENGINES • In a gasoline engine, the speed and power are controlled by the throttle valve, which controls the amount of air entering the engine. • In a diesel engine, speed and power are not controlled by the amount of air entering the cylinders because the engine air intake is always wide open. • Therefore, the engine always has enough oxygen to burn the fuel in the cylinder and will increase speed (and power) when additional fuel is supplied.

10. DIESEL ENGINESIndirect and Direct Injection • In an indirect injection (abbreviated IDI), diesel fuel is injected into a small prechamber, which is connected to the cylinder by a narrow opening. • The initial combustion takes place in this prechamber. Figure 4 - 3

11. DIESEL ENGINESIndirect and Direct Injection • In a direct injection (abbreviated DI) diesel engine, fuel is injected directly into the cylinder. • The piston incorporates a depression where initial combustion takes place. Figure 4 - 4

12. DIESEL ENGINESDiesel Fuel Ignition • Ignition occurs in a diesel engine by injecting fuel into the air charge which has been heated by compression to a temperature greater than the ignition point of the fuel or about 1000°F (540°C). • The chemical reaction of burning the fuel liberates heat, which causes the gases to expand, forcing the piston to rotate the crankshaft. • On the intake stroke, the piston passes TDC, the intake valve(s) open and the fresh air is admitted into the cylinder, and the exhaust valve is still open for a few degrees to allow scavenging to occur.

13. DIESEL ENGINESDiesel Fuel Ignition • On the compression stroke, after the piston passes BDC, the intake valve closes and the piston travels up to TDC (completion of the first crankshaft rotation). • On the power stroke, as the piston nears TDC on the compression stroke, diesel fuel is injected by the injectors, and the fuel starts to burn, further heating the gases in the cylinder. • During this power stroke, the piston passes TDC and the expanding gases force the piston down, rotating the crankshaft.

14. DIESEL ENGINESDiesel Fuel Ignition • On the exhaust stroke, as the piston passes BDC, the exhaust valves open and the exhaust gases start to flow out of the cylinder. • This continues as the piston travels up to TDC, pumping the spent gases out of the cylinder. • At TDC, the second crankshaft rotation is complete.

15. THREE PHASES OF COMBUSTION • There are three distinct phases or parts to the combustion in a diesel engine. • Ignition delay. Near the end of the compression stroke, fuel injection begins, but ignition does not begin immediately.

16. THREE PHASES OF COMBUSTION • Rapid combustion. This phase of combustion occurs when the fuel first starts to burn, creating a sudden rise in cylinder pressure. • Controlled combustion. After the rapid combustion occurs, the rest of the fuel in the combustion chamber begins to burn and injection continues. This is an area near the injector that contains fuel surrounded by air. This fuel burns as it mixes with the air

17. DIESEL ENGINE CONSTRUCTION • Diesel engines must be constructed heavier than gasoline engines because of the tremendous pressures that are created in the cylinders during operation. • The torque output of a diesel engine is often double or more than the same size gasoline-powered engines. • See the comparison chart (next)

18. DIESEL ENGINE CONSTRUCTION

19. DIESEL ENGINE CONSTRUCTION Figure 4 - 5. This engine cutaway shows the heavy construction of a diesel engine. Note the thick cylinder walls and heavy-duty connecting rod

20. FUEL TANK AND LIFT PUMP • A fuel tank used on a vehicle equipped with a diesel engine is different than the one used with a gasoline engine including: • A larger filler neck for diesel fuel. • No evaporative emission control devices or charcoal (carbon) canister. Diesel fuel is not as volatile as gasoline and, therefore, diesel vehicles do not have evaporative emission control devices

21. FUEL TANK AND LIFT PUMP • Many diesel engines also use a fuel temperature sensor. • The computer uses this information to adjust fuel delivery based on the density of the fuel. Figure 4 - 6

22. INJECTION PUMP • A diesel engine injection pump is used to increase the pressure of the diesel fuel from very low values from the lift pump to the extremely high pressures needed for injection. • Injection pumps are usually driven by the camshaft at the front of the engine. • See Figure 4-7 (next)

23. INJECTION PUMP Figure 4 - 7. A distributor-type diesel injection pump

24. INJECTION PUMP Distributor Injection Pump • A distributor diesel injection pump is a high-pressure pump assembly with lines leading to each individual injector. • The high-pressure lines between the distributor and the injectors must be the exact same length to ensure proper injection timing. • See Figure 4-8 and 4-9 (next)

25. INJECTION PUMP Distributor Injection Pump Figure 4 - 8. A schematic of a Stanadyne diesel fuel injection system, showing all of the related components

26. INJECTION PUMP Distributor Injection Pump Figure 4 - 9. The fuel injection lines deliver fuel to the injectors

27. COMMON RAIL FUEL SYSTEM • Newer diesel engines use a fuel delivery system referred to as a common rail design. • Diesel fuel under high pressure, over 20,000 psi (138,000 kPa), is applied to the injectors, which are opened by a solenoid controlled by the computer. • Because the injectors are computer controlled, the combustion process can be precisely controlled to provide maximum engine efficiency with the lowest possible noise and exhaust emissions. • See Figure 4-10 (next)

28. COMMON RAIL FUEL SYSTEM Figure 4 - 10

29. DIESEL INJECTOR NOZZLES • Diesel injector nozzles are spring-loaded closed valves that spray fuel directly into the combustion chamber or precombustion chamber. • Injector nozzles are threaded or bolted into the cylinder head, one for each cylinder, and are replaceable as an assembly

30. DIESEL INJECTOR NOZZLES • The tip of the injector nozzle has many holes to deliver an atomized spray of diesel fuel into the cylinder. Parts of a diesel injector nozzle include: • Heat shield. This is the outer shell of the injector nozzle and has external threads where it seals in the cylinder head.

31. DIESEL INJECTOR NOZZLES • Injector body. This is the inner part of the nozzle and contains the injector spring, needle valve, and threads into the outer heat shield. • Diesel injector needle valve. This precision machined valve and the tip of the needle seal against the injector body when it is closed. • Injector pressure chamber. The pressure chamber is a machined cavity in the injector body around the tip of the injector needle.

32. DIESEL INJECTOR NOZZLE OPERATION • On common rail systems the electric solenoid attached to the injector nozzle is computer controlled and opens to allow fuel to flow into the injector pressure chamber. • See Figure 4-11 and 4-12 (next)

33. DIESEL INJECTOR NOZZLE OPERATION Figure 4 - 11.

34. DIESEL INJECTOR NOZZLE OPERATION Figure 4 - 12

35. DIESEL INJECTOR NOZZLE OPERATION • The ECM can control the injectors according to how it is programmed. For example, the Duramax 6.6 L diesel uses two types of injection pulses: • Pilot injection • Normal injection

36. DIESEL INJECTOR NOZZLE OPERATION • Pilot injection delivers a small amount of fuel just before normal (main) injection at speeds below 2500 rpm. • This helps to improve combustion and reduce noise. Normal injection immediately follows the pilot injection pulse. • See Figure 4-13 (next)

37. DIESEL INJECTOR NOZZLE OPERATION Figure 4 - 13. Fuel delivery occurs in a pilot and main injector pulse

38. GLOW PLUGS • A glow plug is a heating element that uses 12 volts from the battery and aids in the starting of a cold engine. • As the temperature of the glow plug increases, the resistance of the heating element inside increases, thereby reducing the current in amperes needed by the glow plugs.

39. GLOW PLUGS • Most glow plugs used in newer vehicles are controlled by the power train control module (PCM), which monitors coolant temperature and intake air temperature. • The glow plugs are turned on or pulsed on or off, depending on the temperature of the engine. • The PCM will also keep the glow plug turned on after the engine starts to reduce white exhaust smoke (unburned fuel) and to improve idle quality after starting. See Figure 4-14 (next)

40. GLOW PLUGS Figure 4 - 14

41. ENGINE-DRIVEN VACUUM PUMP • Because a diesel engine is unthrottled, it does not create a vacuum in the intake manifold. • Several engine and vehicle components operate using vacuum, such as the exhaust gas recirculation (EGR) valve and the heating and ventilation blend and air doors.

42. DIESEL ENGINE ADVANTAGES • A diesel engine has several advantages compared to a similar size gasoline-powered engine including: • 1. More torque output • 2. Greater fuel economy • 3. Longer service life

43. DIESEL ENGINE DISADVANTAGES • A diesel engine has several disadvantages compared to a similar size gasoline-powered engine including: • 1. Engine noise, especially when cold and/or at idle speed • 2. Exhaust smell • 3. Cold weather startability • 4. Heavier than a gasoline engine.

44. DIESEL ENGINE DISADVANTAGES Figure 4 - 15

45. SUMMARY • A diesel engine uses heat of compression to ignite the diesel fuel when it is injected into the compressed air in the combustion chamber. • There are two basic designs of combustion chambers used in diesel engines. Indirect injection (IDI) uses a precombustion chamber whereas a direct injection (DI) occurs directly into the combustion chamber. • The three phases of diesel combustion include: • Ignition delay • Rapid combustion • Controlled combustion

46. SUMMARY • The typical diesel engine fuel system consists of the fuel tank, lift pump, water-fuel separator, and fuel filter. • The engine-driven injection pump supplies high-pressure diesel fuel to the injectors. • The two most common types of fuel injection used in automotive diesel engines are: • Distributor-type injection pump • Common rail design where all of the injectors are fed from the same fuel supply from a rail under high pressure. • Injector nozzles are either opened by the high-pressure pulse from the distributor pump or electrically by the computer on a common rail design. • Glow plugs are used to help start a cold diesel engine and help prevent excessive white smoke during warm-up.

47. REVIEW QUESTIONS 1. What is the difference between direct injection and indirect injection? 2. What are the three phases of diesel ignition? 3. What are the two most commonly used types of automotive diesel injection systems? 4. Why are glow plugs kept working after the engine starts?

48. ASE CERTIFICATION-TYPE QUESTIONS 1. How is diesel fuel ignited in a warm diesel engine? a. Glow plugs b. Heat of compression c. Spark plugs d. Distributorless ignition system

49. ASE CERTIFICATION-TYPE QUESTIONS 2. Which type of diesel injection produces less noise? a. Indirect injection (IDI) b. Common rail c. Direct injection d. Distributor injection

50. ASE CERTIFICATION-TYPE QUESTIONS 3. Which diesel injection system requires the use of a glow plug? a. Indirect injection (IDI) b. Common rail c. Direct injection d. Distributor injection