The two cycle engine is notorious for producing pollution.

So far, I don't see this being addressed. Sure a smaller four-stroke will be better on fuel economy and therefore on overall emissions, but the hefty pollution price paid during two-stroke acceleration is dad news.

Will this take cars back to the old "blue-smoker" days?

John:  You're thinking of 2-cycle engines which breathe through the crankcase and are lubricated by oil mixed with the fuel.  This engine is nothing like that.

A piston-ported 2-stroke isn't compatible with the Atkinson cycle, but this engine has hydraulic poppet valves.  It would appear simple to control cylinder air charge by varying the delay on intake-valve closure, though this might create difficulties with turbocharger surging unless the turbo also had a waste gate.

An engine which performs much of its compression with a turbocharger and requires no throttle under most load conditions would be highly efficient.

John: You're thinking of 2-cycle engines which breathe through the crankcase and are lubricated by oil mixed with the fuel. This engine is nothing like that.

And due to direct injection fresh fuel cannot escape through the exhaust before combustion, because the exhaust valve will be closed when fuel is injected.

Also in a 2-cycle engine without valves the intake and exhaust timing is symmetrical and exhaust port always closes after intake port.

If this engine was only driven in 2 cycle mode it could make a nice engine for a series/plug-in hybrid.

(more power less weight and less volume).

I have the same concern as Rafael regarding practical emission control of NOx and excessive heat problem.

Direct-injection and turbocharged 4-stroke engines today are already very powerful, having 100 hp/liter specific power rating. Specific output is more limited by heat rejection and engine durability rather than any other factors. I don't see how much a 2-stroke mode will add to improve power output when heat and durability are still the limiting factors in engine downsizing.

It is possible to run this engine using gasoline stoichiometrically in 2-stroke mode if the exhaust valve is closed right after blowdown, before the intake valve will be opened any significant length of time, hence, no escape of free air (O2), but there still the heat problem to be dealt with due to the very high EGR (Exhaust gas recirculation) ratio, as the exhaust gas remaining in the cylinder will be very hot, forcing late injection of gasoline at near TDC to prevent pre-ignition, and then we will have to deal with higher PM emission, and maybe high NOx also (?), due to the residual heat in the EGR, and higher cost of high-pressure gasoline direct injection system, and the higher cost of electro-hydraulic valve system. A blower is still needed to force air into the cylinder in the 2-stroke mode, so no saving there, either.

I still think electric-ICE hybridization offers the most practical, efficient and cost-effective engine downsizing of any other options for engine downsizing.

My 1972 Kawasaki H2 750cc 3cyl 2-stroke went into HCCI mode accidentally once. It was weird, I pulled out the key and it would not shut off.

I don't see how much a 2-stroke mode will add to improve power output when heat and durability are still the limiting factors in engine downsizing.

At least one advantage of the 2-cycle over 4-cycle is, that the BMEP can be lower at the same power output. This means maximum forces on piston, rods and crankshaft are also lower at the same power output - which again means a reduction in engine weight.

A turbo will deliver scavenging air but not as much boost pressure as in the case of a four stroke, so power is not doubled.

The advantage of doing this with a diesel is that the internal EGR and blown-through air don't matter nearly as much, and the reduction in size (and probably cylinder count) would cut both weight and cost; going from 4 injectors to 3 cuts 25% of that costly section.  If you could get reasonable acceleration and even towing performance in a full-size minivan with a 1.5 liter engine, the savings in fuel could be dramatic.

globi stated:

"At least one advantage of the 2-cycle over 4-cycle is, that the BMEP can be lower at the same power output. This means maximum forces on piston, rods and crankshaft are also lower at the same power output - which again means a reduction in engine weight."

I'm for this if it can produce >160hp/liter. 177-180hp/liter seems to be the max for the production vehicles at this point. Assuming the 27% efficiency gains are from downsizing and DI vs a larger NA with PI, its no better than a new Mitsubishi Lancer Evolution X GSR FQ-360. Mahle has a great downsized turbo gasoline engine concept, though with a less extreme 163hp/liter.

As for NOx and PM concerns, a hydrogen supplementation system, like one from Hy-Drive (albeit smaller and lighter), may do the trick. Replacing the Lead acid battery with a NiMH or Li-ion, and a small motor/generator connected to the powertrain would provide the necessary electrical energy via regenerative braking. One may even add an onboard water distillation systems utilizing waste heat.

The baseline vehicle for the study was an 1800 kg passenger car sold in the European market with a 3.5 litre naturally aspirated V6 gasoline engine and 5 speed conventional automatic transmission with torque converter. In other words your basic gas guzzler I suppose.
The simulation results indicate that vehicle acceleration performance, including launch from rest, can be maintained with a 2.0 litre V6 2/4SIGHT gasoline engine replacing the 3.5 litre baseline powerplant.

I hate to rain on anyone's parade here, my studies on gasoline engines have revealed that if you halve the stroke of any engine. Then, providing the new bore/ stroke ratio doesn't exceed 1.5 which usually it does not, then you can run the new engine at twice the rpm, but getting only half the torque of course. You will be back where you started with the exact same power but doing it with only half the literage. Thus I debunk the old saying "There's No Replacement For Displacement" And since the stroke is being reduced by only 50mm, in this case, it doesn't save much weight in an engine that may be around 500mm tall. Bottom line - a 2.0L V6 saves almost nothing over a 3.5L V6 since both of these powerful engines could be just idling, at the same rpm, while propelling the vehicle at a nominal road speed of 65mph.

In case you are wondering what they might have done instead. Just a minute while I drop the tone arm on the record. " The suggestion is that one way to downsize is to simply reduce the number of cylinders but be sure to maintain the same TOTAL piston area as before by enlarging piston diameters. You can prevent the bore/stroke ratio from exceeding 1.5 by increasing the stroke to suit. Finally top rpm speed for the engine will be when the MEAN piston speed approaches 20m/sec (4000fpm). This rpm, of course, is dependent on the stroke length you chose earlier.

This suggestion comes from the result of examining 50 engines from different manufacturers scrutinizing their output figures against their dimensions to discover correlations. Correlation was found in close agreement when considering naturally aspirated fuel injected engines."
T2