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  Exhaust gas: Two stroke engine



You may ask what this age-old concept is doing in a book about exhaust gases. Whether the examples of bad exhaust gas should be presented here again and whether we want to reintroduce the bad air caused by Trabi engines and Russian engine oil in the cities of the ex-GDR.

No, be sure, we want the exact opposite, clean air and low CO2 emissions. How is that supposed to work? A basic consideration: If you look closely, then downsizing is already approaching limits. One has reached three cylinders, but you can hardly get any smaller, because a two-cylinder four-stroke basically behaves like a single cylinder.

This can then only be remedied somewhat with balancer shaft(s). Fiat tries, but where is the savings effect then? VW seems to have already given up, no longer offers anything below 2 liters for diesel and is partially rationalizing away the 1.8 for gasoline in favor of the two-liter. Has downsizing almost failed here?

But if you assume four cylinders with two liters of displacement, you end up with three cylinders with 1.5 liters (BMW/Mini). How nice would be two cylinders with a total displacement of 1 liter? As a two-stroke engine, the two pistons would run in push-pull and thus balance each other out much better. And if engine builders already earlier constituted a third liter displacement as ideal for a cylinder, that would even be possible.

You almost stopped reading because you cannot get by with so little expected performance? But you should know that a two-stroke engine theoretically has almost twice as much power as a four-stroke engine, including torque. If a turbocharger were to be added, would you yet continue here?

We can only think of two-stroke engines with direct injection, as gasoline engines anyway. Is old hat (Gutbrod, 50s) you will say. Yes, but at that time it was not intended to be downsized and neither not combined with charging. We want valves that open so that a turbocharger blows through sometimes one cylinder and then the other. If exhaust gas is to remain, then it is intentional and map-controlled.

And the injection always starts immediately after the valves close, regardless of how long it lasts. Maybe even an idea earlier, the main thing is that no unburned fuel gets into the exhaust. And since we already mentioned Fiat, we are further developing their concept of valve opening by hydraulics so that we no longer need a camshaft.

It's going to be a very difficult part, okay. Are 300 to 350 bar enough to open and close valves safely against springs? Would that also work with the fuel from the rail and additional, strictly separated oil lubrication of the components? Or could the high pressure pump generate high oil pressure at the same time? It would be great if you could also generate swirl with individually controlled valves.

Of course, the geometric compression would have to be much higher than today's gasoline and diesel engines. One would regulate near the knock limit simply by closing the valves in good time and less injection. Lambda would always remain close to 1, particularly complex exhaust gas aftertreatment is not necessary. With natural gas, this engine even enters the regenerative age.

You are right, in relation to the displacement, it will still be a very expensive engine, especially if the turbocharger were also given an additional electric drive a la Formula 1. Less or no more turbo lag and, if possible, no accumulation when accelerating. There would be space for further hybrid technology, preferably directly from Toyota without clutch and multi-step transmission (picture above). Programming the necessary software for this should not be easy, however.







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