What Is a Forward Start Option?

When the engine (gasoline engine) is working, the ignition timing has a great influence on the working performance of the engine. Pre-ignition is the ignition of the spark plug before the piston reaches the top dead center of compression, igniting the combustible mixture in the combustion chamber. From the moment of ignition until the piston reaches the top dead center of compression, the angle that the crankshaft rotates during this period is called the ignition advance angle. The ignition advance angle at which the engine can obtain the best power, economy and optimal emissions is called the optimal ignition advance angle.

Chinese name: Ignition advance angle

Ignition advance angle effect

The mixture in the cylinder burns at a certain speed, that is, it takes time for the spark plug to flash and the combustible mixture in the cylinder completely burns, but because the engine speed is high, the crankshaft can rotate very large in such a short time. angle. If the ignition happens when the piston reaches the top dead center and the mixture starts to burn, the piston has already started to move downwards, resulting in a decrease in the power of the engine. Therefore, it is necessary to ensure that the energy generated by the combustible mixture can be effectively used by improving the engine's performance Output Power.

When the gasoline engine keeps the throttle opening, speed and mixture concentration constant, the gasoline engine power and fuel consumption rate change with the ignition advance angle. There is an optimal ignition advance angle for each operating condition of the engine.

Proper ignition advance angle allows the engine to do the most mechanical work per cycle (the shaded part of the curve)

The ignition advance angle is too large, which is easy to deflagrate;

The ignition advance angle is too small, the exhaust temperature rises, and the power decreases. ^[1]

Effect of ignition advance angle on engine maximum combustion pressure

Ignition advance angle

There is a time process from the ignition, combustion to burnout of the mixture. The effect of the optimal ignition advance angle is to make the maximum expansion trend of the gas in the piston work down stroke under various conditions. This results in the highest efficiency, minimal vibration, and lowest temperature rise. In order for the maximum combustion pressure in the engine cylinder to appear at 10 ° to 15 ° after the end of compression to maximize the combustion power of the mixture, it must be ignited at an appropriate time before the end of compression.

In theory, the minimum ignition advance angle is 0 degrees, but in order to prevent the mixture from being ignited during the power stroke (this will cause a loss of power), it is often set to more than 5 degrees, which is also the angle required to start the rotation speed. The maximum ignition advance angle cannot be too large, and generally cannot exceed 60 degrees, otherwise the problems of vibration and temperature rise will be highlighted, and the efficiency will also be reduced. In fact, the speed of the crankshaft structure is limited.

Influencing factors of ignition advance angle

The factors that affect the ignition advance are the speed and the combustion speed of the mixture. As the speed increases, the time to turn the same angle becomes shorter, and only the larger advance angle can get the corresponding advance time. The combustion speed of the mixture is related to the composition of the mixture, the structure of the engine, and other factors, such as the shape of the combustion chamber and the compression ratio.

Premature ignition will cause knocking, the piston will be blocked from moving upward, the efficiency will be reduced, and heat load, mechanical load, noise and vibration will increase, which should be prevented. Ignition is too late, gas is difficult to do work, high fuel consumption, low efficiency and loud exhaust sound. No matter if the ignition is too early or too late, it will affect the speed increase. The optimal ignition angle is affected by many factors. If you want your car to work in an ideal state, the following factors must be considered:

1. Cylinder temperature and pressure. The higher the burning speed, the smaller the ignition advance angle. Factors affecting cylinder temperature and pressure include: engine compression ratio, air temperature, cylinder temperature, and load. Everyone's car behaves differently in the season when the temperature changes.

2. Gasoline octane number. That is to say, the higher the anti-knock ability, the higher the ignition advance angle.

3. Gas mixing ratio. Excessive rich and lean burn speeds are slow, you need to increase the ignition advance angle. This mainly depends on the throttle opening and altitude.

For unpredictable situations, some cars are also equipped with a knock sensor, which automatically reduces the ignition advance angle when knocking occurs.

Obviously, to complete such a complex modulation, traditional analog igniters are incompetent. Only the single-chip igniter can achieve the optimal ignition advance angle at high speed, accuracy and stability.

Ignition advance angle adjustment basis

The optimal ignition advance angle is mainly related to engine speed, load, fuel type (such as gasoline grade) and other influencing factors.

1. When the engine throttle is constant, as the rotation speed increases, the ignition advance angle needs to be increased, but when the rotation speed reaches a certain value, the increase of the optimal ignition advance angle is slowed down, instead of maintaining the same increase speed.

2. When the engine speed is constant, as the load increases, the throttle opening degree increases, and the ignition advance angle needs to be appropriately reduced. On the contrary, when the engine load decreases, the ignition advance angle should be appropriately increased.

3. Fuel type: Different gasoline brands have different octane numbers. The octane number indicates the violent performance of gasoline. When using gasoline with higher octane number, that is, better explosion resistance, the ignition advance angle should be increased.

Other factors: Some other factors in the engine will affect the combustion speed of the mixture. These factors will affect the ignition advance angle, such as the shape of the combustion chamber, the temperature in the combustion chamber, the air-fuel ratio, the atmospheric pressure, and the temperature of the cooling water.

Ignition advance angle check adjustment

Ignition advance angle check, adjustment of platinum contacts

Check the platinum contacts for signs of burnout. If there are marks, use sand strips or No. 0 sandpaper to gently wipe them off. As the contact surface of the platinum contact has only a thin layer of cemented carbide, if the cemented carbide is worn away for a long time, then the contact should be replaced, and the contact surface of the contact should not be less than 80%. The gap of platinum contacts is generally 0.4 ~ 0.5mm.

Check ignition advance angle , adjust ignition advance angle

Remove the vacuum hose in the auxiliary chamber from the vacuum advance compensation device, and block the two ports connected to the hose to allow the engine to run at idle speed. At this time, check the ignition advance angle with the ignition timing lamp. For TJ376Q and TJ370Q engines, the ignition advance angle is 5 ° + 2 ° (850 + 50f / min); for JL368Q engines, the ignition advance angle is 7 ° (900r / min); for CFGFda462Qv engines, the ignition advance is 10 ° + 1 ° (900r / min); for the 276Q engine, the ignition advance angle is 6 ° + 2 ° (900r / min).

The ignition advance angle can be adjusted by a special distributor housing method. When the distributor housing is turned counterclockwise, the ignition advance angle will increase; when the distributor housing is turned clockwise, the ignition advance angle will decrease.

Ignition advance angle

Start the engine and repeatedly press the accelerator pedal. If you feel the engine is strong and there is no abnormal tapping sound, it indicates that the ignition advance angle is appropriate. You can also use the timing light to confirm the ignition advance angle: as the engine speed increases, the timing mark will move in the direction that the ignition advance angle increases.

Ignition advance angle adjustment method

Ignition advance angle mechanical centrifugal and vacuum adjustment device

The engine speed and load are constantly changing, and each operating condition corresponds to an optimal ignition advance angle. In order to make the engine change in a timely manner under different operating conditions, the following three ignition devices are generally provided.

(1) Centrifugal ignition advance adjustment device

When the engine speed changes, it automatically changes the phase relationship between the breaker cam and the distributor shaft, and changes the ignition advance angle. The weight is used to increase the centrifugal force with the increase of the rotation speed, and the spring force is thrown out against the spring force. The linkage advances the cam on the shaft by an angle to increase the ignition advance angle. This device works when the crankshaft speed is 400-1500r / min.

(2) Vacuum ignition advance adjustment device

When the engine load, that is, the throttle opening degree changes, the ignition advance angle is automatically adjusted. The change of the opening degree of the throttle valve is used to change the surrounding vacuum degree, and the distributor housing, the fixed plate and the contact point are moved backward by an angle to increase the ignition advance angle through the vacuum chamber and its linkage device. This device does not work when the throttle opening is maximum (full open) and minimum (close to full closed).

(3) Octane number corrector

The octane corrector is a device for manually adjusting the ignition advance angle when changing the type of fuel.

When the engine is changed to gasoline with a different octane number, this device is used to change the initial ignition time (the aforementioned two automatic adjustment devices work on this basis). It also uses the method of changing the phase relationship between the contact and the cam to adjust the ignition advance angle.

Electronic ignition control system for ignition advance angle

The electronically controlled ignition system senses the influence of various factors on the ignition advance angle through various sensor signals, so that the engine can obtain the optimal ignition advance angle when the speed and load are changed, compared with mechanical and vacuum ignition advance angle adjustment devices. The electronically controlled ignition system is more accurate and is a leap forward in the development of ignition systems.

The electronically controlled ignition system controls the ignition advance angle from starting conditions and normal conditions. The following is the control method of the ignition advance angle:

1.Starting condition control

During starting conditions, the signal of the absolute pressure sensor of the intake pipe or the signal of the air flow meter is unstable, and the ECU cannot correctly calculate the ignition advance angle. Generally, the ignition timing is fixed at the set initial ignition advance angle. When the ECU detects that the engine is in the starting condition, it controls the ignition of each cylinder according to a preset initial ignition advance angle. The control signals used at this time are the engine speed signal (Ne signal) and the start switch signal (STA signal). The setting of the initial ignition advance angle varies depending on the engine, and is generally about 10 degrees before the top dead center of compression.

2. Normal operating conditions of the engine

Idling

The ECU determines the basic ignition advance angle based on the throttle position sensor signal (IDL signal), the engine speed sensor signal (Ne signal), and the air conditioning switch signal (A / C signal).

Operating conditions other than idle

The ECU determines the basic ignition advance angle based on the engine speed and load (intake or unit injection quantity per revolution), and corrects the ignition advance angle based on signals measured by actual sensors, including warm-up correction and overheating correction. , Idle speed stability correction, air-fuel ratio feedback correction, etc.

The ECU will control the ignition advance angle in real time according to the parameter value measured by the sensor, and set the ignition advance angle limit adjustment function to limit the actual ignition advance angle not exceeding the set allowable value. ^[2]

Determination of basic ignition advance angle