One big complaint about hybrids is they often don't have enough power. Has anyone done anything with 2 engine designs? A mid sized sedan would have one
12 hp reciprocating engine and maybe another 50 hp engine.At first glance the biggest problem seems to be rigging all this together without getting to complicated, expensive or heavy.
Bret Cahill
A 2 engine series hybrid.
Bret Cahill
I had an idea sort of similar only using a single engine. Sorta played around with some diagrams too. I don't know if anyone else has done research on this... but:
What about a small 4-stroke engine that has the plumbing to allow it to convert to a 2-stroke engine when additional power is needed?
Say your sedan has a 75 hp motor, but when you need the power or acceleration (which is probably less than 1% of time), it goes to
2-stroke and...say... 140 hp? It'd save alot of gas in the long run (smaller motors *generally* operate more efficiently than larger motors for various reasons). The decreased efficiency of the 2-stroke is minimal (considering it would be used rarely), and is offset by the gas saved with a smaller, more efficient engine AND reduced weight.Dave
Ignition wouldn't be a problem. Fuel injection wouldn't be a problem. Two fuel tanks, a main tank and a two stroke oil gas mix tank wouldn't be a problem.
For 2 stroke mode, solenoids could deactivate push rods or rocker arms to close all the intake and exhaust valves at the same time.
Alternatively the cam shaft could be moved axially so every poppet valve slides off cam.
Solenoid valves opening 2 stroke ports wouldn't be a problem.
Computer controls do everything now anyway so nothing should be a problem.
It's hard to believe no one has thought of this before.
Must be something with the bore/stroke ratio or some other difficult to change aspect of 4 strokes that is different than 2 strokes.
Very though provoking idea. I'm sure you'll get more replies.
Bret Cahill
snipped-for-privacy@gmail.com (David Harper) >
2 stroke mode might not be twice the power but it could be enough for many applications, not just motor vehicles.Search
It's hard to believe everyone on the well traveled path of reciprocating engines overlooked this.
Bret Cahill
Ten year old Patent 5,517,951 has computer operated valves. Any number of cylinders can be 2 stroke while the rest are 4 stroke.
I'm guessing that the power boost isn't worth it because it seems like a better idea than the other way: shutting down half the cylinders altogether which has appeared several times on production V-8 models.
Someone needs to go to DOE, get a grant, and prove one way or another if the 2 stroke mode gives a power boost > 50%
Bret Cahill
Well, stop me if I'm wrong... but anything operating in 2-stroke mode should theoretically get "almost" twice the power that a 4-stroke engine would get at the same RPM (holding everything else constant). Instead of every other stroke providing torque (as in 4-stroke), it's EVERY stroke, thereby effectively doubling the torque, and the power output (P=torque * speed). 2-stroke isn't as efficient, as you generally don't have complete exhaustion of combustion products, pre-ignition mixing isn't great, incomplete combustion, etc. Also, you need to cool more aggressively.
The main advantage of 2-stroke is a better power/weight ratio than
4-stroke. Generally, they're also simpler and cheaper (i.e. great for lawnmowers, weedwackers, etc).Dave
But everything else might not be able to be held constant. There might be something that needs to be changed for optimum operation that is difficult to switch.
Supercharging can provide small fuel efficient engines with additional on demand power. By increasing the effective compression ratio they are probably increasing the efficiency. It may be hard to compete against supercharging with an engine that drops to a much lower efficiency.
That's why when Otto started pushing for
4-stroke, everyone thought he was nuts. ("You want to WASTE a cycle?")
You aren't getting a full charge of air, no matter how much gas you are willing to waste.
. . .
The idea should be pursued. Like I said it sounds better than the other way: shutting down 4 cylinders of a V-8 altogether. Even if it doesn't make sense now it may in the next decade or so.
Some turbo charger guy told me he went to a Honeywell conference last year and all the turbo chargers were sized for 1.3 liter engines. He asked why and they said "$4.00/gallon gas."
Bret Cahill
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