 Exhaust gas 2
Crazy, right? 'Curing' one pollutant with another. No, not crazy at all, because 'afterburning' only fixes what was previously spoiled due to a lack of time and insufficient mixing. But there is one important condition attached to
this process: All components must be present in the correct mass ratio. And that only works with a lambda of 1.
A truck can also have a three-way catalytic converter, like the one pictured above. While diesel engines can't use it, trucks, or rather buses, can have natural gas engines. They also have a correct electric spark ignition
system and a very large-displacement gasoline engine. And they always need a catalytic converter like this.
Yes, there is a deliberate circumvention of the Lambda-1 rule. This stems from the gasoline engine's obligation to reduce fuel consumption and increase of efficiency, after its mission to reduce harmful emissions was
largely considered fulfilled. During this phase, the diesel engine experienced the exact opposite: It was considered economical, but not sufficiently low-emission.
Interestingly, these requirements have brought gasoline engines closer to diesel engines in terms of technology. In addition to the switch from manifold to direct injection, the advantages of which you can read about in the
book on gasoline injection, swirl formation has also been increasingly used. The idea behind this is to provide the spark plug with a sufficiently ignitable mixture and to distribute a lean mixture throughout the rest of the
combustion chamber.
The formation of layers in the combustion chamber was born, but it's actually not a new topic. Do you notice how we're slowly approaching the lambda value of 1.4 found in diesel engines? The technologies for achieving
this, however, are diverse, new, and correspondingly difficult. Just imagine: A piston is supposed to achieve a precisely prescribed, uneven distribution of mixture in the combustion chamber at speeds of 1,000 to 6,000
rpm and under a wide range of loads.
Of course, it's not just the piston that's involved. This includes the position of the valves, the entire intake system, and even the placement of the injector. The piston contributes with a piston crown that sometimes dwarfs
the complexity of a cavernous landscape (pictured below). Somehow, some of the air returns to the spark plug and is supplied with sufficient fuel either there or near it upon entry.
kfz-tech.de/PVe62
If the impression arises that this process is underused, it's worth correcting. Since the automotive industry doesn't seem to encounter insurmountable difficulties, the process is being used, partly because the EU is
exerting pressure with its CO2 regulations.
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