Cars, computers and fitness. Three areas of knowledge a modern man has to know. Lets tackle CARS in this post!
Normal cars in Melbourne can run on:
1. gasoline (unleaded gasoline with RON values 91/95/98 = the octane rating, the higher the octane, the better and stronger the engine runs). Leaded gasoline have high octane rating (lead is added to boost the octane rating), but lead is toxic, it goes out in the exhaust and can cause mental issues for children who inhale it;
2. diesel – requires a diesel engine. Diesel engine doesn’t need spark, it spray the diesel into a hot compressed air.
3. LPG (liquid petrol gas)/ autogas – is either propane (C3H8) or butane (C4H10) or mix of these 2. The autogas can be compressed into liquid. An odorant is added to autogas to make it easy to detect if there is a leak.
Most of the engines use Internal combustion. Internal combustion principle: if we put a tiny amount of high-energy fuel in an enclosed space and ignite it -> incredible energy in expanding gas… To have this phenomenon happening hundreds of time in a second = car engine.
How Engine Works (Otto invented in 1867) – 1 Cylinder process.
There are 4 strokes of the piston:
1. Intake stroke: open the intake valve, a tiny amount of gasoline goes in.
2. Compression stroke: the piston goes up, compressing the air for stronger effect.
3. Combustion stroke: the ignition sparks, causing the explosion, pushing the piston.
4. Exhaust stroke: the exhaust valve opens, piston goes up to push the exhaust out of cylinder (will go to tailpipe).
Using the crankshaft to convert linear motion (the piston) to rotational motion (for the wheels).
Most cars have 4, 6 or 8 cylinders (xi-lanh).
Blue part = connecting rod. Green part = crankshaft (trục quay) . Inside the cylinder we have spark plug providing spark.
Camshaft: (trục phân phối – trục quay để cho valve vào và van ra mở ra đúng thời điểm).
The camshaft is geared to turn at one-half the rate of the crankshaft.
Camshaft quay nửa vòng thì valve thứ hai mở ra, quay một vòng thì lai mở valve số 1 – một vòng quay của Camshaft thì mỗi valve mở một lần = piston lên xuống 2 lần (mỗi 2 stroke là 1 lần piston lên xuống – crankshaft 1 vòng = 2 stroke, camshaft quay 1 vòng = 4 strokes). Camshaft quay chậm = 1 nửa crankshaft.
A timing belt or timing chain links the crankshaft to the camshaft so that the valves are in sync with the pistons. – cái băng này đồng điệu hai trục quay, để valve mở ra đúng thời điểm.
Many high-performance engines have four valves per cylinder (two for intake, two for exhaust), and this arrangement requires two camshafts per bank of cylinders, hence the phrase “dual overhead cams.”
C. Engine Problems:
There are 3 main problems: bad fuel mix, lack of compression, lack of spark.
1. Bad Fuel Mix:
- Out of gas: the engine got air but no fuel.
- Air intake clogged: fuel but no air
- Too much or too little fuel
- Impurity fuel (like water in gas tank) – fuel can’t burn
2. Lack of Compression:
- Piston rings are worn (air/fuel leaked from piston)
- Intake or exhaust valve not sealing – air leaked
- Hole in cylinder: most common hole in cylinder is at the head of cylinder (where the spark plug attaches to cylinder). The cylinder and the cylinder’s head has a gasket between to avoid leak. When the gasket breaks down -> holes between cylinder & head -> leaks.
3. Lack of spark:
- Spark plug (or the wire leading to it) worn out -> weak spark
- Wire is cut: no spark.
- Ignition timing off: the spark occurs either too early or too late in the cycle, the fuel will not ignite at the right time, and this can cause all sorts of problems.
4. Other problems:
- Battery dead: ắc-qui không có điện =
- No oil: -> piston can’t move freely ->
- ống khói tắc (bị bịt)
- Valves open not at the right time -> air ko vào được hoặc khí thải ko ra được = engine chết.
- Bearings (ổ trục chống ma sát) của crankshaft bị mòn -> trục quay ko quay được!