3.2 The four-stroke diesel engine
Most diesel engines use the same four-stroke
combustion cycle that one could observe with petrol engines, with a caveat: diesel
engines compress air at much higher levels, and when air is compressed, it
heats up. Since the air in diesel-engine cylinders is higher than diesel fuel’s
“auto-ignition” temperature, no spark plug is required to get you moving.
Here is the process:
- Stroke 1: Air Intake. The opening of the intake valve allows fresh air to enter the combustion chamber. The piston moves down as air enters.
- Stroke 2: Compression. The piston compresses the air in the cylinder by moving back up. Compression ratios from 15:1 to 25:1 are the most common ones.
- Stroke 3: Combustion. When the air is compressed enough at a high enough temperature, fuel is injected into the cylinder, where it immediately combusts. This creates the power which is channelled through the crankshaft to move the vehicle forward. It also pushes the cylinder back down.
- Stroke 4: Exhaust. A fourth and final stroke pushes the exhaust gas out of the exhaust valve to make room for more fresh air.
FOUR-STROKE DIESEL ENGINE
Problems with diesel engines can be very daunting when you begin to experience diesel problems, especially when you’re unfamiliar with the machinery. Issues with diesel engine parts can occur through wear and tear, but sometimes these issues can be more complex. This handy guide explores the most common problems with diesel engines so that you can be prepared and aware in the unfortunate event that you experience difficulty with different diesel engine parts. The most common diesel problems can be split into two categories which mostly overlap: issue-specific and part-specific.
The four most frequently occurring issue-specific problems are:
1. Engine overheating
2. Oil leakages
3. Oil supply problems
Now, let’s discuss each of these problems in more details.
1. Engine overheating
The number one problem found in diesel engines is engine overheating. It happens when an engine is pushed too hard and can give rise to a whole host of negative side-effects. This includes, but is not limited to:
• Damage to the bearings and crankshaft.
• Pistons expanding and scraping against cylinder walls (crushing the cylinder head gasket in the process).
• Cylinder heads swelling, distorting and breaking.
2. Oil leakages
Oil leaks stem largely from issues with diesel engine parts, such as aged seals and gaskets which no longer work effectively. If left unattended, oil leaks can cause serious diesel problems, as they pose both an environmental threat and serious fire risk and can result in complete engine failure.
3. Oil supply problems
Oil supply problems
predominantly stem from either incorrect oil use or a lack of oil. Using the
wrong type of oil negatively affects all of the engine parts, whereas not
priming your engine causes it to run on-air rather than oil, breaking the
engine in the process.
Diesel engines parts known to have problems
The most frequently occurring diesel problems concern the following key engine parts, many of which (although not all) are in conjunction with the issues above:
Pistons are an important part of the engine and can fail in several ways. These include:
• Piston rings wearing out.
• Knocking.
• Soot deposits on the piston crown.
• The piston becoming cracked (caused by frequent use of poor quality fuel).
Gaskets
The most frequent cause of failure in gaskets is overheating via coolant leaks. However, in general, diesel engines are more prone to gasket failure than other engine types, largely because diesel gaskets regularly face higher combustion pressures. Repair of diesel gaskets is made all the more complicated (although not impossible) by the intricate nature of diesel engines.
Cylinder heads
Problems related to cylinder heads are usually categorised by loss of compression. Cracks in cylinder heads which lead to leakages are also a common issue, as are internal casting defects.
Bearings face a lot of stress due to the daily friction they experience- insufficient lubrication can therefore lead to bearing (and consequently engine) failure. Other causes of bearing damage include an improper selection of bearing material for the engine type at hand.
Most of the common problems with diesel engines will incorporate a mixture of the above issues and affected diesel engine parts. However, it must be emphasised that the above offers a simple overview only, and additional diesel problems certainly exist. Each issue is multi-faceted, with parts affected and displayed in numerous ways.