Why is the spark ignited just before TDC and not at TDC?

Why is the spark ignited just before TDC and not at TDC?

Just before top dead center (TDC) the spark plug fires to start combustion. With a rich air/fuel mixture this starts burning very rapidly and the peak firing pressure will be higher than normal and also closer to TDC. At times this detonation will create so much heat that the air/fuel mixture can auto-ignite.

What causes ignition timing to advance?

Advancing the timing means the plug fires earlier in the compression stroke (farther from TDC). Advance is required because the air/fuel mixture does not burn instantly. It takes time for the flame to ignite the all the mixture.

What does referring to ignition timing mean TDC?

relative to top dead center
Ignition timing refers to the angular position of the crankshaft relative to top dead center (TDC) that is the crankshaft angular position at which the piston is at the exact top of the compression stroke.

Why does the optimum ignition timing change with engine operating conditions?

The timing advance occurs when the ignition occurs earlier in the compression stroke, i.e., before the Top Dead Centre (TDC). However, if the spark advances too much, then the combustion will complete even before the piston reaches the TDC. Thus, it allows sufficient time for burning the air-fuel mixture.

How do I know if my ignition timing is too advanced?

When any changes are made to the engine of a car, the ignition timing is adjusted accordingly. If not, you could experience several problems with your engine with improper ignition timing like knocking, hard to start, increase fuel usage, overheating, and reduced power.

What happens if timing is too far advanced?

Overheating. If ignition timing is too far advanced, it will cause the fuel-and-air mixture to ignite too early in the combustion cycle. This can cause the amount of heat generated by the combustion process to increase and lead to overheating of the engine.

What happens if ignition timing is off?

What causes ignition timing to be off? When any changes are made to the engine of a car, the ignition timing is adjusted accordingly. If not, you could experience several problems with your engine with improper ignition timing like knocking, hard to start, increase fuel usage, overheating, and reduced power.

What is the correct ignition timing?

The ideal ignition timing for power occurs just before the point where detonation or pinging takes place. Correctly timed ignition will cause peak cylinder pressures to occur around 12 to 15 degrees after TDC.

What should timing be at idle?

The timing can vary between 2 and 12 degrees BTDC, the recommended spark plugs are different and even the plug gaps vary. In most cases starting out with 12 degrees of initial advance is about right. The initial timing should be 4 degrees before top dead center (BTDC).

How do I know if my timing is advanced?

Symptoms of a Bad or Failing Automatic Timing Advance Unit

1. Engine knock. One of the earliest symptoms of a problem with the automatic timing advance unit is engine knock.
2. Sluggish performance. Another symptom of a problem with the automatic timing advance unit is sluggish engine performance.
3. Excessive black smoke.

Why is spark initiated before top dead center?

Examples: Setting the ignition timing, so that the spark is initiated before top-dead-center, is necessary because of the time delay before the explosion reaches maximum force. The objective is to ensure the piston has begun its downward (power) stroke as the expanding gases reach their maximum pressure.

When does ignition advance occur in a car?

Ignition Advance is the difference between this moment and the occurrence of the spark. The timing advance occurs when the ignition occurs earlier in the compression stroke, i.e., before the Top Dead Centre (TDC). However, if the spark advances too much, then the combustion will complete even before the piston reaches the TDC.

How to advance your ignition timing for great performance?

The first step in advancing your ignition timing is to dive underneath the bonnet to locate the diagnostics box. For the purposes of these steps, I’ll be using the images from a very helpful guide uploaded onto MX-5 Nutz.

How does ignition timing affect mean effective pressure?

The above figure shows that Indicated Mean Effective Pressure (IMEP) tends to increase with ignition timing advance between 21 and 41° BTDC. It is expected that IMEP should increase with timing angle advance to a point, and then drop off. Best performance will be achieved when the greatest portion of the combustion takes place near top dead center.