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 Quality/Quantity 2
kfz-tech.de/PVe64
So you can't supply the gasoline engine with the same amount of air every time, regardless of the amount of fuel. Therefore, the air and fuel supply must always be regulated. This is called
'quantity control' because, unlike with diesel, the composition (quality) remains the same, but the total amount (quantity) changes.
So you have to throttle back, which means you lose a small percentage of efficiency compared to a diesel engine. In addition, to achieve the best possible balance of pollutants in the three-way catalytic
converter, the vehicle
operates at Lambda=1, even though Lambda=1.05 would be more fuel-efficient. That's where the diesel engine has another advantage.
The fact is that here, every carbon atom has more than one oxygen atom to choose from, and so it finds one quickly enough, least when the rotational speed isn't too high. In a gasoline engine, the oxygen
atoms associated with carbon are, in principle, counted by a lambda value of 1 and are therefore harder to detect, although with more time.
The term "afterburning" used to describe the oxidation process in the downstream three-way catalytic converter is questionable. So it compensates for the combustion that did not take place. This is good for
emissions figures, but it somewhat masks the loss of efficiency in the combustion chamber. It would have been better if the burning had taken place there as well.
None of that is likely to happen to a diesel engine. There, neither the airflow needs to be throttled, nor is there much left to burn after during mixture formation. Now you might understand why, as a good part-
load fuel-efficient vehicle, it was first used in passenger cars that served as taxis. They focused on the low fuel consumption and overlooked the sluggish, loud, and jerky acceleration.
By the way, the taxi industry has taken another factor into account. The diesel engine handled the frequent cold starts better. Because if as much fuel as possible is burned, there is less to dilute the oil. That
has changed a bit in the meantime. This is because when additional fuel is injected to remove nitrogen oxides, oil dilution and even ash buildup in the DeNOx catalyst are possible.
Well, it's high time we do something for the gasoline engine, too. Because we are now reaching higher engine speeds. Things are getting tight for diesel engines, too. In the past, it produced a significant amount of
soot when running at full throttle. Black smoke is a clear sign of a lack of oxygen. Meanwhile, the gasoline engine maintains its finely balanced mixture.
Things are getting even worse for the diesel engine. Since it ignites immediately (on its own) upon injection, this process cannot be extended indefinitely. The gasoline engine can also form a fuel-air mixture for a much
longer period of time as a direct-injection engine. Now the pros and cons are reversed: The diesel engine does not reach the maximum RPM of the gasoline engine.
After all, in passenger car diesel engines, 5,000 rpm, and even a bit more, is now possible again. Here, the introduction of direct injection initially resulted in a significant reduction in rated speeds. So it’s recovered a bit
from that in the meantime. However, when you compare it to high-revving gasoline engines, the difference can be enormous.
What motorcycle enthusiast, apart from certain cruiser fans, would be satisfied with the revs of a diesel engine? What was the absolute top speed in Formula 1 again? Almost 20,000 rpm? Incidentally, a diesel engine can
easily become a high-consumption fuel consumer if its engine speed is excessively high. It is interesting to note, however, that gasoline engines, especially those with turbochargers, have recently begun to approach
diesel engines in terms of rated speed.
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