Injection: lean mixture / stratified charge
Modern gasoline engines prefer direct injection to reduce fuel consumption. Indeed, the fact of installing the injector directly in the room allows control (according to the calculator) more precisely fuel supply to cylinders.
It also saves money while the engine is running. down et average speed, it is possible to inject fuel in a different way without the driver noticing it. And this is where the multilevel charging process comes in.
In passing, note that the letter S of Volkswagen Group FSI engines stands for laminate.
Instead of constantly injecting fuel during acceptance stage For a 4-stroke engine, this operating mode consists of injecting a dose of fuel into compression moment cycle, i.e. later (note that some fuel is still injected during suction).
Result, mix not homogeneous in the cylinder, as this could not be done during air intake. Fuel focused on a small area just below the injector when it is about to catch fire, it allows to reduce consumption and combustion temperature (no need to fill the entire chamber). Note that the decrease in consumption is due to the fact that this process limits the dose delivered, allowing the gasoline engine to run with excess air, which also limits pumping losses (since gasoline has a throttle valve to measure the amount of fuel / oxidant mixture). Because in the case of conventional injection, the fuel / oxidizer mixture must not contain too much air for the assembly to ignite correctly (stoichiometric ratio). To simplify, the fact of the need to limit the volume of air in the cylinders causes a "vacuum effect" at the level of the engine (pumping losses), which takes up some of its power (it is a butterfly that modulates in a continuous flow of air. Power gauge). A phenomenon not found in a diesel engine. Thus, in stratified mode, we open the butterfly completely without the pumping effect that takes up energy and therefore fuel!
Unfortunately, this injection mode results in imperfect fuel combustion. An inhomogeneous mixture causes NOx and fines. And when a diesel engine uses a particulate filter, it is cleaner in terms of particulate emissions than a gasoline engine that does not.
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Abderrahmane (Date: 2019, 12:29:20)
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