Diesel engines may seem mystifying to the average person. But understanding the basic components that make up these workhorse engines empowers truck owners to make informed maintenance decisions.
In this beginner’s guide, as a professional diesel engine parts supplier, I’ll overview the critical parts and systems that allow a diesel engine to convert chemical energy into rotational mechanical force.
What are the Main Parts of a Diesel Engine?
The Cylinder Block: The Foundation
The heavy cylinder block forms the backbone of a diesel motor. This thick casting usually made from cast iron or aluminum alloy bears the brunt of combustion.
The block has cylindrical holes called, of course, cylinders. Inside these cylinders, fuel ignites and pistons pump to produce power.
The upper portion of cylinder blocks also provides a mounting point for cylinder heads. And the crankcase at the base contains vital components like the camshaft.
Fun Fact: Cylinder sleeves or liners slide inside the cylinder bore to protect the block’s walls from piston rings scraping away metal.
Pistons Transfer Power
Sliding up and down inside each cylinder is a piston. These quick-moving parts play a crucial role.
As expanding gases push down on a piston’s crown, the connected rods relay linear motion to the rotating crankshaft below. This smoothly converts up and down reciprocatory action into rotational energy used to propel the vehicle.
Consequently, piston rings prevent pressurized gases from escaping into the crankcase during combustion cycles. This maintains efficiency.
Connecting Rods Join Forces
Connecting rods connect pistons to the crankshaft. At the bottom is the crankpin bearing surface. At the top is the wrist pin bushing for the piston.
Durability is a must here due to extreme operating pressures. So most connecting rods consist of steel I-beam forgings able to withstand 55,000 psi stresses at up to 6,000 rpm.
Crankshafts Turn Linear into Rotational
The heavy crankshaft sits snugly inside the crankcase at the base of the cylinder block. As each rod journal receives rotating force from a connecting rod, the off-center throws of the crank amplify this energy.
The crankshaft also holds counterbalance weights to offset vibrating forces. It runs on sturdy main bearings and uses oil passages for lubrication.
Cylinder Heads Seal Combustion Chambers
Sitting atop each cylinder is a cylinder head. These close off the top of the cylinders to form combustion chambers between their lower deck face and the top or crown of each piston.
Heads have intake and exhaust valve ports along with other passages for delivery of fuel and airflow. Coolant also flows through for cooling.
They bolt down onto the cylinder block using a head gasket to ensure a tight seal capable of withstanding over 2,000 psi of compression.
Valvetrains Time Combustion
A diesel engine’s valvetrain consists of components that operate the cylinder head’s poppet valves. They precisely time opening and closing events relative to piston movement.
Most diesel valvetrains have pushrods and rocker arms driven by overhead camshafts. But a few use solenoids for valve actuation.
Regardless of their configuration, precise valve timing and duration is critical to engine efficiency.
Camshafts Orchestrate Valves
Overhead camshafts control intake and exhaust valve opening and closing events. These precision shafts have eccentrically mounted lobes that translate rotary motion into linear action.
Timing chains, belts, or gears turn the camshafts which follow specific profiles to properly sequence valve events. This allows for ideal combustion timing and exhaust scavenging.
Fuel Injection Systems Spray Combustible Mixtures
Diesel fuel must atomize into tiny droplets to ignite. Cummins, Navistar, DMax, PowerStroke and other diesel engines use specialized high pressure common rail fuel injection systems to achieve combustion.
These complex assemblies use electronic fuel injectors to precisely meter fuel amounts and injection timing. Fuel pressurizing can reach 30,000 psi to properly atomize diesel for ideal power, efficiency and emissions.
Glow Plugs/Grid Heaters Assist Cold Starting
Unlike gasoline motors, diesels rely on heat to autoignite compressed air and diesel mist. Glow plugs and grid heaters help get things cooking.
These electric heating elements have a hot coil at the tip that warms the combustion chamber. Once started, heat of compression then sustains ignition.
Turbochargers Cram More Air In
Nothing beats forced induction when it comes to making power. And most modern diesels use a turbocharger to boost intake air density.
These clever air pumps have a turbine wheel driven by exiting exhaust gases, spinning an impeller forcing more air into cylinders. Variable vane turbines (VGT) and multiple turbo arrangements allow tuning for power or economy.
Intercoolers Cool Compressed Intake
Increasing air density raises its heat which reduces power. Most force induction engines use an intercooler to remove heat from the compressed air enroute from the turbo into the engine.
Usually air-to-air units, popular intercooler types include bar and plate, tube and fin, and extruded tube designs. Large heat exchange surface areas combined with heat absorbing aluminum alloy construction drops intake temperatures.
Oil Systems Grease and Cool Critical Parts
Diesels have high performance oiling systems to lubricate, cool and clean critical components. Multi-grade oils work with oil filters and coolers to properly lubricate engines.
High fuel pressures in injector systems require extremely precise injector lubrication. So most diesel engines have specialized injector lubrication with tighter tolerances preventing wear.
Cooling Systems Regulate Engine Temperatures
Coolant jackets surround cylinders helping carry off combustion heat energy via circulating coolant. This liquid passes through radiators and thermostatically controlled water pumps to maintain optimum operating temperatures.
Diesel cooling systems pressurize to increase heat carrying capacity. They also have deaeration tanks and recovery reservoirs to minimize coolant loss. Proper pH and rust inhibitors are critical as well.
Exhaust Components Scavenge Burnt Gases
Once combustion converts fuel into rotating force, exhaust gases exit into exhaust manifolds routing them out of cylinder heads.
Components like turbochargers, diesel particulate filters (DPF), catalytic converters, and mufflers treat hot gases before releasing into the atmosphere.
Proper exhaust system sizing, heat management, and backpressure control ensures both power and regulatory compliance.
In Summary
And there you have it. While relatively simple in concept, modern diesel engines use some complex yet durable parts to convert fuel into work over billions of combustion cycles.
Knowing this basic anatomy helps owners better understand service requirements. It also empowers you to make educated repair decisions confidently.
Understanding how any machine works takes much of the mystery out of owning and operating it. If you found this guide helpful or have comments, let me know!