Geely JL481Q, Manual

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An operational cycle of 4-stroke engine is made of the intake, compression, power and exhaust strokes. When the
piston moves from Top Dead Center (TDC) to the Bottom Dead Center (BDC), the crank turns 180°. The distance from
TDC to BDC is called piston stroke.
1. Intake Stroke
The intake stroke is the process of taking in the combustible gas mixture into the cylinder. The intake valve opens right
before the piston approaches the TDC, and the exhaust valve closes immediately after the piston goes down. The intake
and exhaust valves form a proper overlap angle when they’re open simultaneously, which helps emitting the exhaust gas
effectively and improving the scavenge quality with the gas inertia. As the piston goes down further, the gas capacity
expands to produce ultra vacuum in the cylinder, so more gas mixture is taken in. When the piston reaches the BDC, the
intake valve is still open. Till the piston goes up and more combustible gas mixture goes into the cylinder with inertia, the
intake valve will close after the crank turns to the proper delay angle.
If the operational capacity of cylinder is fixed, in order to enable the engine to produce more power, the gas mixture
shall be taken in as much as possible in the intake stroke. In this sense, multiple valves, turbine mid-air cooler and
electronic fuel injector are applied to produce more high-quality combustion gas mixture
2. Compression Stroke
The compression stroke is the process of compressing the combustible gas mixture in the cylinder. The piston goes up
from the BDC, with the intake and exhaust valves closed. The pressure and temperature of combustible gas mixture in the
cylinder increase rapidly, so the heat-atomized fuel and gas become more even that helps improving the combustion
quality and the power capability. As improving the compression pressure may result in certain danger, the compression
ratio shall be keep at the best level. Improving properly the engine compression ratio, i.e. the ratio of maximal cylinder
capacity vs post-compression minimal capacity, may make the engine more powerful and cost-effective.
3. Power Stroke
The power stroke is the process in that the combustible gas mixture burns and expands to generate power in the
cylinder. At this moment, the intake valve is still closed. Before the piston goes up the TDC, the temperature and pressure
of gas mixture increase a lot, which drives the ECU to select and figure out the best ignition timing, and then the spark plug
will generate spark to ignite the combustible gas mixture. The gas mixture burns and releases heat that makes the
temperature and pressure increase sharply in the cylinder, and the maximal pressure occurs at the crank angle of 10° to
20° after reaching TDC. When the piston goes down after reaching the TDC, the expansion-to-power process begins. The
piston drives the crank and flywheel rotating with the connecting rod, and outputs the driving torque. When the piston
reaches the BDC, the power stroke ends. In order to keep the engine more powerful, cost-effective and less-polluting, we
have made great efforts to improve the combustion, make full use of the fuel, and purify the exhaust gas, and we’ll go on
with the efforts
4. Exhaust Stroke
The exhaust stroke is the process of emitting exhaust gas out of the cylinder. Before the piston goes down to the BDC
in the power stroke, the exhaust valve opens, and the hot combustion gas turns to be exhaust gas after the expansion-to-
power process, and then begins to go out of the cylinder. The piston goes up after it reaches the BDC, and the exhaust gas
is extruded. Before the piston reaches the TDC, the intake valve begins to open for scavenge. Of course, when the piston
reaches the TDC, the exhaust valve will close after a period of delay.
The piston goes down from the TDC into a new operational cycle. With the operational cycles made up of the above-
mentioned 4 strokes, the engine works repeatedly and outputs non-stop power that drives the car forward