start Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 19, the reader should be able to: • • • • Prepare for ASE Engine Performance (A8) certification test content area “C” (Fuel, Air Induction, and Exhaust Systems Diagnosis and Repair) Explain how a diesel engine works Describe the difference between direct injection (DI) and indirect injection (IDI) diesel engines Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 19, the reader should be able to: • • • • List the parts of the typical diesel engine fuel system Explain how glow plugs work List the advantages and disadvantages of a diesel engine Describe how diesel fuel is rated and tested Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: API gravity • cetane number • cloud point diesel oxidation catalyst (DOC) • differential pressure sensor (DPS) • Direct injection (DI) flash point • glow plug heat of compression • high-pressure common rail (HPCR) • hydraulic electronic unit injection (HEUI) indirect injection (IDI) • injection pump • lift pump opacity • pop tester • regeneration • water-fuel separator Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 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 fuel, so it requires no spark ignition system The diesel requires ratios of 16:1 and higher Incoming air is compressed until its temperature reaches about 1000°F (540°C), called heat of compression The piston reaches the top of its compression stroke, fuel is Figure 19–1 Diesel combustion occurs when injected into the cylinder, fuel is injected into the hot, highly compressed air in the cylinder where it is ignited by hot air Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 As the fuel burns, it expands and produces power Because of the very high compression and torque output of a diesel engine, it is made heavier and stronger than the same size gasoline-powered engine A common diesel engine uses a fuel system precision injection pump and individual fuel injectors The pump delivers fuel to the injectors at a high pressure at timed intervals Each injector sprays fuel into the combustion chamber at the precise moment required for efficient combustion Figure 19–2 A typical injector-pump-type automotive diesel fuel injection system Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman Continued ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 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 The air–fuel mixture of a diesel can vary from as lean as 85:1 at idle to as rich as 20:1 at full load 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 not suffer from throttling losses Throttling losses involve power needed in a gasoline engine to draw air past a closed or partially closed throttle In a gas engine, speed and power are controlled by the throttle valve, which controls the amount of air entering the engine Adding more fuel to the cylinders of a gasoline engine without adding more air (oxygen) will not increase the speed or power of the engine Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 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 Diesel engines are built in both two-stroke and four-stroke versions The most common two-stroke diesels were the truck and industrial engines made by Detroit Diesel In these engines, air intake is through ports in the cylinder wall Exhaust is through poppet valves in the head A blower pushes air into the air box surrounding liner ports to supply air for combustion and to blow the exhaust gases out of the exhaust valves Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Indirect and Direct Injection In an indirect injection (IDI) diesel engine, 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 This has the effect of slowing the rate of combustion, which tends to reduce noise Figure 19–3 An indirect injection diesel engine uses a prechamber and a glow plug Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 All indirect diesel injection engines require the use of a glow plug 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 Direct injection diesel engines are generally more efficient than indirect injection engines, but have a tendency to produce greater amounts of noise While some direct injection diesel engines use glow plugs help cold starting and to reduce emissions, many direct injection diesel engines not use glow plugs Figure 19–4 A direct injection diesel engine injects the fuel directly into the combustion chamber Many designs not use a glow plug Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 10 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 White Smoke White exhaust smoke occurs most often during cold engine starts because the smoke is usually condensed fuel droplets White exhaust smoke is also an indication of cylinder misfire on a warm engine The most common causes of white exhaust smoke: Inoperative glow plugs Low engine compression Incorrect injector spray pattern A coolant leak into the combustion chamber Gray or Blue Smoke Usually due to oil consumption caused by worn piston rings, scored cylinder walls, or defective valve stem seals Can also be caused by a defective injector(s) Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 66 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SCAN TOOL DIAGNOSIS Diesel engines since the late 80s have been computer controlled and equipped with sensors and activators to control functions previously mechanically controlled All light truck diesels since 1996 have also adhered to on-board diagnostic systems (2nd generation [OBD-II]) The use of a scan tool to check for diagnostic trouble codes (DTCs) and to monitor engine operation is one of the first diagnostic steps Figure 19–20 A scan tool is used to retrieve diagnostic codes and perform injector balance tests Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 67 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 COMPRESSION TESTING Fundamental for determining mechanical condition of a diesel engine Worn piston rings can cause low power and excessive exhaust smoke A diesel engine should produce at least 300 psi (2,068 kPa) of compression pressure and all cylinders should be within 50 psi (345 kPa) of each other Figure 19–21 A compression gauge designed for the higher compression rate of a diesel engine should be used when checking the compression Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 68 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 GLOW PLUG RESISTANCE BALANCE TEST Glow plugs increase in resistance as temperature increases All glow plugs should have about the same resistance when checked with an ohmmeter A similar test of the resistance of the glow plugs can be used to detect a weak cylinder, particularly helpful on a diesel engine that is not computer controlled To test for even cylinder balance using glow plug resistance, perform the following on a warm engine: Unplug, measure, and record resistance of all of glow plugs With wires still removed from the plugs, start the engine Allow the engine to run for several minutes to allow the combustion inside the cylinder to warm the glow plugs Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 69 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Measure the plugs and record the resistance of all of the glow plugs The resistance of all of the glow plugs should be higher than at the beginning of the test A glow plug that is in a cylinder that is not firing correctly will not increase in resistance as much as the others Another test is to measure exhaust manifold temperature at each exhaust port Misfiring cylinders will run cold This can be done with a contact or noncontact thermometer Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 70 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 INJECTOR POP TESTING A pop tester is a device used for checking a diesel injector nozzle for proper spray pattern The handle is depressed and pop off pressure is displayed on the gauge The spray pattern should be a hollow cone This will vary depending on design The nozzle should also be tested for leakage—dripping of the nozzle while under pressure If the spray pattern is not correct, cleaning, repairing, or replacing of the injector nozzle may be necessary Figure 19–22 A typical pop tester used to check the spray pattern of a diesel engine injector Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 71 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Always Use Cardboard to Check for High Pressure Leaks If diesel fuel is found on the engine, a high-pressure leak could be present When checking for a high-pressure leak, wear protective clothing including safety glasses and face shield plus gloves and long-sleeved shirt Then use a piece of cardboard to locate the high-pressure leak When a Duramax diesel is running, the pressure in the common rail and injector tubes can reach over 20,000 psi At these pressures the diesel fuel is atomized and cannot be seen but can penetrate the skin and cause personal injury A leak will be shown as a dark area on the cardboard When a leak is found, shut off the engine and locate the exact location of the leak without the engine running CAUTION: Sometimes a leak can actually cut through the cardboard, so use extreme care Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 72 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 DIESEL EMISSION TESTING The most commonly used diesel exhaust emission test used in state or local testing programs is the opacity test Opacity means the percentage of light that is blocked by the exhaust smoke A 0% opacity means the exhaust has no visible smoke and does not block light from a beam projected through the exhaust smoke A 100% opacity means the exhaust is so dark that it completely blocks light from a beam projected through the exhaust smoke A 50% opacity means the exhaust blocks half of the light from a beam Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 73 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Snap Acceleration Test The vehicle is held stationary with wheel chocks and brakes released as the engine is rapidly accelerated to high idle with the transmission in neutral while smoke emissions are measured Conducted a minimum of six times and the three most consistent measurements are averaged together for a final score Rolling Acceleration Test Vehicles with a manual transmission are rapidly accelerated in low gear from an idle speed to a maximum governed RPM while the smoke emissions are measured Stall Acceleration Test Vehicles with automatic transmissions are held stationary with the parking brake and service brakes applied while transmission is placed in “drive.” The accelerator is depressed and held momentarily while smoke emissions are measured The standards for diesels vary according to the type of vehicle and other factors, but usually include a 40% opacity or less Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 74 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Do Not Switch Injectors In the past, it was common practice to switch diesel fuel injectors from one cylinder to another when diagnosing a dead cylinder problem However, most high-pressure common rail systems used in new diesels use precisely calibrated injectors that should not be mixed up during service Each injector has its own calibration number See Figure 19–23 Figure 19–23 The letters on the side of this injector on a Cummins 6.7-liter diesel indicate the calibration number for the injector No switch injectors Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 75 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 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: a Ignition delay b Rapid combustion c Controlled combustion Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 76 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY (cont.) 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: a Distributor-type injection pump b Common rail design where all of the injectors are fed from the same fuel supply from a rail under high pressure Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 77 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY (cont.) 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 The higher the cetane rating of diesel fuel, the more easily the fuel is ignited 10 Most automotive diesel engines are designed to operate on grade #2 diesel fuel in moderate weather conditions Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 78 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY (cont.) 11 The API specific gravity of diesel fuel should be 30 to 39 with a typical reading of 35 for #2 diesel fuel 12 Diesel engines can be tested using a scan tool, as well as measuring the glow plug resistance or compression reading to determine a weak or nonfunctioning cylinder Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 79 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 end Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 80 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458