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A turbocharged car engine with electronically activated intake and exhaust valves, that can switch from 4 stroke cycle to 2 stroke cycle when the turbocharger is providing boost, thereby nearly doubling the power output.
The engine would operate as a normal 4 stroke at low throttle settings. At
higher throttle settings, when the turbo is producing enough boost to scavenge the cylinders with both the intake and exhaust valves open simultaneously, the engine would operate as a two stroke (I believe this is how a turbo 2 stroke diesel locomotive works, but it uses an auxiliary compressor for starting). Apparently electronic valving is now being produced by some auto manufacturers. This allows the separate throttle valve to be done away with, along with the associated turbulence losses and extra boost lag it introduces. Also, direct injection into the combustion chamber could be used to prevent unburned fuel from being swept out the exhaust when 2-stroking, thereby reducing the emmisions normally associated with 2 strokes. For further improvement a Comprex pressure wave supercharger could be used instead of a turbo, allowing increased boost at low engine speeds.
Camless variant
http://waw.wardsaut...k_ma_no_4/index.htm
Lotus hydraulic-electric valve actuation [riccoman, Oct 17 2004]
Gasoline direct injection
http://www.mitsubis...logy/GDI/page5.html
Mitsubishi direct injection system [riccoman, Oct 17 2004]
Pressure wave supercharger
http://www.swissaut...4?ID_Display=200004
Swiss Hyprex pressure wave supercharger project [riccoman, Oct 17 2004]
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2 strokes are generally less efficient than the common 4 stroke engine, with a higher noise output. ANother problem this poses is you now need a timing system more advanced than the honda v-tec. Since you are switching from 4 to 2, the timing is faster and will work your cams faster, so without a sophisticated program, its useless. |
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Assuming the inefficiency in 2 strokes you're referring to is due to unburned fuel being lost out the exhaust, the direct injection could avoid this inefficiency. |
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Regarding cams, there would be none thanks to the electronically activated solenoid valves (perhaps I didn't explain this well enough). All timing would be done by the ECU (engine control unit). |
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As for noise, I'm sure it would increase, but hey, that's an attraction for some (but not me). |
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So if I understand this correctly, you're suggesting that when an extra burst of power is needed, the valve timing changes to open the exhaust valves just before BDC to start the exhaust flow, and then the intake valves would open shortly thereafter (with the exhaust valves still open). Then the exhaust valves would close and some time after that the fuel injectors would kick in. Am I understanding you correctly? |
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Sounds pretty reasonable to me. The overlapped intake and exhaust cycles would waste a fair amount of energy as some of the work spent compressing the intake air would go to waste, but I would expect that the power would increase anyway. I'd guess that you'd spend fuel twice as fast as normal to get maybe a 50% boost in power. Obviously not a very efficient way to run the engine most of the time *BUT* if having the two-stroke mode available allowed the use of a 25% smaller engine, the efficiencies gained there might offset the occasional inefficiencies of two-stroke mode. |
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The biggest technical obstacles I can see are (1) switching smoothly between two- and four-stroke mode; and (2) having acceptable and useful fuel/air and compression ratios in both modes. The percentage of oxygen in cylinder air is going to be lower in two-stroke mode than in four-stroke mode, and the compression ratio is likely to be lower as well. Perhaps leaving the intake valve open for a ways past BDC in four-stroke mode would allow the TDC volume to be reduced enough to allow an adequate compression ratio in two-stroke mode. |
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Yes, that's pretty much the idea. There probably would be a real kick in the pants when switching to 2 stroke, but perhaps the lower compression and oxygen levels at that stage would offset this. If not, the ECU could throttle things back a little during transition. Of course, 2 stroke mode could be disabled with a switch or something too. |
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One of the classic marine and loco 2-
stroke diesels was supercharged and
opposed-piston, so was able to provide
scavenging by blowing a puff of air in
ports at one end of the combustion
chamber and force the exhaust out
ports the other end. |
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This was the Deltic. No valves, no cams,
no sparks, no cylinder head. I bet with
modern electronic injection
this would be a honey. |
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Why have 4 strokes at all when you can
work with 2? At low revs such diesels
have huge grunt. |
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I haven't read all the annotations, but the first few covered the same questions I had after reading half of the idea. If the solenoid-operated valve technology is mature and reliable enough to make the timing work, this could work well. |
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The idea here is not for efficiency, but rather for a high-power burst when needed (correct me if I'm wrong). By effectively doubling the number of power strokes per revolution, the wasted efficiency would be more than made up for. |
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Bun for the extra power, bone for the extra pollution, so my vote stays neutral. |
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Take this engine and stuff it into a hybrid electric car, run it in 4 stroke mode (assuming this mode is more fuel-efficient) at the point of optimum fuel efficiency to charge the batteries and provide power to the electric traction motor. When maximum power is required switch the mode to 2 stroke and up the revs to the point of max power output and route power from the battery and alternator to the traction motor. Or better yet, make the point of max power and max fuel efficiency the same. |
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Freefall: Why would pollution have to be worse, given modern engine controls and catalytic convertors? |
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actually, most of the tech is in place if you built tyhis as a diesel , 2 stroke diesels with solenoid valves already exist.if your crank was built right you could also switch to a 6 or 8 stroke mode for extended idling |
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Hey Riccoman, check out the 2004 SAE World Congress at popular mechanics. Riccardo,Inc. is trying to put the engine into production. Maybe you are associated with Riccardo,Inc? |
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I've wondered for ages why 2 stroke (with the ports and simelar method used by ships etc) is not being used by cars. You would be much better going for a diesel as they already have forced induction for the most part. The only problem here is your fancy valve timing. A number of companies are looking at solenoids, BMW for example, the problem being that 12V electronics are not able to deliver the power at the same time as being compact. Assuming that electonic valve actuation gets sorted out soon, and I'm sure it will, you're also not thinking big enough. Why stop at 2/4 stroke? You can have 2/4/6/8 whatever stroke, or even a mixture of all with one cylinder running 2 stroke and 3 running 4 stroke or whatever mix is the most efficient given the speed and power requirements. With fancy routing you can even get one cylinder exhausting into another, add a fraction of the fuel and use another cylinder to make sure everything from the first is burnt. |
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Whoever commented about V-tec, it's great, but when you have an ECU controlling the valves the possibilities are much greater. |
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