Engines and Engine Systems

Motors and Engine Systems

Module Introduction

This chapter covers all the knowledge required for the Red Seal exam concerning diesel and gasoline engines used in heavy equipment. You must master operating principles, components, diagnostic procedures, efficiency calculations, and applicable Canadian standards. This module represents approximately 20% of the exam questions, making it the most important in terms of weighting.

Engine Operating Principles

The Four-Stroke Diesel Cycle

The diesel engine operates on the four-stroke cycle invented by Rudolf Diesel. Each complete cycle requires two revolutions of the crankshaft (720°).

Critical point: In a diesel engine, air is compressed to a ratio such that its temperature reaches 500 °C to 700 °C, causing auto-ignition of the injected fuel. There is no spark plug.

The Otto Cycle (Gasoline)

The gasoline engine uses a spark plug to ignite the air-fuel mixture. The compression ratio is lower (8:1 to 11:1) to prevent auto-ignition (knock).

Fundamental Differences

Main Engine Components

The Cylinder Block

The cylinder block is the main body of the engine. It must withstand combustion pressures (up to 180 bar in modern engines) and thermal stresses. The bores are machined with a precision of approximately 0.01 mm.

Wear Check: Measure the bore using a three-point bore gauge in two perpendicular axes and at three different heights. Compare with manufacturer specifications. The maximum allowable ovality is generally 0.05 mm to 0.10 mm depending on the engine.

The Cylinder Head

The cylinder head contains the valves, injectors (or spark plugs), and coolant passages. It is fastened to the block by head bolts tightened to a precise torque and specific sequence.

Tightening Procedure: Always follow the spiral sequence from the center outward. Tighten in three passes: 50%, 75%, then 100% of the final torque. For torque-to-yield bolts, replace them systematically.

The Head Gasket

The head gasket ensures the seal between the block and the cylinder head. Signs of failure include:

Leak Test: Use a cooling system pressure tester and an exhaust gas analyzer in the expansion tank. The presence of CO₂ in the coolant confirms a gasket leak.

The Crankshaft and Bearings

The crankshaft converts the linear motion of the pistons into rotary motion. The main bearings support the crankshaft in the block, and the connecting rod bearings connect the rod to the crankshaft.

Bearing Clearance: The typical oil clearance is 0.025 mm to 0.075 mm for main bearings. Use Plastigage to measure this clearance during assembly.

Clearance Calculation:

Clearance = Journal diameter − Mounted bearing inside diameter

Fuel Injection System

The Injectors

The injector must atomize the fuel into fine droplets (10 to 50 microns) and distribute it uniformly in the combustion chamber. The injection pressure varies according to the technology:

The Injection Pump

The injection pump must deliver fuel at the correct pressure and at the precise time. Injection timing is expressed in degrees before top dead center (BTDC).

Typical Timing: 10° to 25° BTDC depending on speed and load. Overly advanced timing causes knocking; overly retarded timing reduces power and increases exhaust temperature.

The Common Rail System

The common rail system uses a high-pressure accumulator common to all injectors. The injectors are electronically controlled by solenoids or piezoelectric actuators.

Advantages:

Injector Flow Rate Calculation

Flow rate (L/min) = Injected volume (mm³/stroke) × Number of strokes/min ÷ 1,000,000

Example: An injector delivers 120 mm³ per stroke at 2,000 rpm. The flow rate is:

120 × 2,000 ÷ 1,000,000 = 0.24 L/min

Cooling System

Function and Components

The cooling system maintains engine temperature between 82 °C and 98 °C. Components include:

The Thermostat

The thermostat opens at a specific temperature (generally 82 °C to 88 °C) and is fully open at approximately 95 °C. A faulty thermostat can cause:

Test: Place the thermostat in hot water with a thermometer. Check the opening temperature and the total opening travel (generally 8 to 10 mm).

Coolant

Coolant is a mixture of water, ethylene glycol (or propylene glycol), and corrosion inhibitors. The recommended ratio is 50/50, offering protection down to −37 °C and a boiling point of 108 °C with a 100 kPa pressure cap.

System Pressure: Each 1 bar of pressure raises the boiling point by approximately 25 °C. The typical radiator cap is calibrated at 0.5 to 1.0 bar.

Lubrication System

Role of Engine Oil

Engine oil must:

Oil Classifications

The API (American Petroleum Institute) classification uses two letters: the first indicates the type (S for gasoline, C for diesel), the second indicates the performance level.

SAE Viscosity: The SAE classification indicates viscosity. Multigrade oils (e.g., 15W-40) offer protection at both low and high temperatures. The first number (15W) indicates cold-temperature viscosity, the second (40) at 100 °C.

The Oil Pump

The oil pump is generally of the gear or rotor type. It must maintain a pressure of 30 to 60 psi (200 to 400 kPa) at cruising speed.

Minimum Oil Pressure: 10 psi (70 kPa) per 1,000 rpm is a general rule. Lower pressure indicates bearing wear or a faulty pump.

Intake and Exhaust System

The Turbocharger

The turbocharger uses exhaust gas energy to compress intake air. It increases engine power by 30% to 50% without increasing displacement.

Key Parameters:

Axial Clearance: The turbocharger bearing axial clearance must be 0.025 to 0.100 mm. Excessive clearance indicates wear and a risk of wheel/housing contact.

The Charge Air Cooler (CAC)

The CAC cools the air compressed by the turbocharger, increasing its density and therefore engine power. A temperature drop from 100 °C to 40 °C increases air density by approximately 20%.

Leak Test: Apply a pressure of 10 to 15 psi (70 to 100 kPa) in the intake circuit and check for leaks with a soapy solution.

The EGR System (Exhaust Gas Recirculation)

EGR reduces nitrogen oxide (NOₓ) emissions by cooling the combustion. A portion of the exhaust gases is reintroduced into the intake.

Common Problems:

Electrical and Electronic System

The Charging Circuit

The alternator produces alternating current (AC) converted to direct current (DC) by the rectifier. The charging voltage must be 13.8 to 14.4 volts.

Charge Test: Measure the voltage at the battery terminals with the engine at idle. It must be above 13.5 V. At 2,000 rpm, it must not exceed 14.8 V.

Engine Sensors

The Engine Control Module (ECM)

The ECM controls injection, timing, boosting, and emissions. It uses calibration maps (tables) to determine optimal parameters based on operating conditions.

Fault Codes: Diagnostic codes are standardized according to SAE J1939. Codes are structured as follows:

Example: SPN 100 (engine oil pressure), FMI 1 (signal low) indicates oil pressure that is too low.

Diagnostics and Troubleshooting

Engine Compression

The compression test measures the maximum pressure reached in each cylinder. Typical values for a diesel engine are 2,800 to 3,500 kPa (400 to 500 psi).

Procedure:

Interpretation: The difference between cylinders must not exceed 10%. A low value in one cylinder adjacent to another indicates a faulty head gasket. Two adjacent weak cylinders suggest a head gasket between them.

The Leak-Down Test

This test measures the percentage of leakage from a pressurized cylinder. It helps locate the source of the leak.

Locating Leaks:

Exhaust Gas Analysis

The opacimeter measures the opacity of diesel engine exhaust gases. Legal limits are set by each province, but the reference standard is generally 30% to 40% opacity at full load.

Causes of Black Smoke:

Causes of Blue Smoke:

Causes of White Smoke:

Canadian Standards and Regulations

Canadian Electrical Code

The Canadian Electrical Code, Part I (C22.1) applies to electrical installations. For heavy equipment, the relevant provisions concern charging and starting circuits.

Rule 8-200: This rule concerns the calculation of electrical demand for motors. It specifies that a motor's rated current must be based on the nameplate, and that the branch circuit must be protected in accordance with the requirements.

CSA B149.1

The CSA B149.1 standard (Natural Gas and Propane Installation Code) applies to engines operating on natural gas or propane. Requirements include:

Emissions Standards

Diesel engines in heavy equipment must meet Transport Canada emissions standards, aligned with US EPA standards:

Preventive Maintenance Procedures

Oil Analysis

Oil analysis is an essential predictive diagnostic tool. Parameters analyzed include:

Metal Interpretation:

Valve Clearance

Valve clearance must be checked and adjusted according to manufacturer specifications. Incorrect clearance causes:

Typical Clearances:

Procedure: Turn the engine to TDC of cylinder No. 1 at the end of the compression stroke. Adjust the valves according to the firing order. Use a feeler gauge and a torque wrench for the locknut.

The Fuel Filter

The fuel filter must be replaced at the recommended interval (generally 250 to 500 hours). A clogged filter causes:

System Bleeding: After replacing the filter, bleed the air from the system using the manual or electric priming pump. Never start the engine with air in the high-pressure circuit.

Useful Calculations and Conversions

Displacement

Displacement (L) = (π × bore² × stroke × number of cylinders) ÷ 4

Example: Bore = 110 mm, stroke = 130 mm, 6 cylinders

Displacement = (3.1416 × 0.11² × 0.13 × 6) ÷ 4 = 0.0074 m³ = 7.4 L

Compression Ratio

Compression ratio = (Total volume) ÷ (Combustion chamber volume)

Total volume = Chamber volume + Volume swept by the piston

Power

Power (kW) = Torque (N·m) × Angular velocity (rad/s)

Angular velocity = (2 × π × rpm) ÷ 60

Example: Torque = 1,200 N·m at 1,500 rpm

Power = 1,200 × (2 × 3.1416 × 1,500 ÷ 60) = 1,200 × 157.08 = 188.5 kW

Common Conversions

Pitfalls to Avoid

Summary

Self-Assessment Questions

This chapter covers the essential knowledge for the "Motors and Engine Systems" section of the Red Seal exam. Review the figures, tables, and procedures before moving on to the practice questions.