Do combustion engines all turn in the same direction?
Are there some that don’t?
All the lawn mowers I see discharge on the right, is there a reason?
I thought of a lawnmower with counter rotating engines, discharging on both sides. Wouldn’t that be more efficient?
“Efficient”? In what sense of the word? A pair of 2-horsepower engines is bulkier, heavier, and more expensive than a single 4-horsepower engine. And probably less fuel-efficient, too. What benefit did you have in mind?
No, they can turn either way.
Some, depending on design can even be reversed.
Yes.
Because they spin clockwise, it it ejected from the left, it would be blowing forwards, and the wind would blow it up and back into your face.
No, because unless both blades are isolated, you will have competing vortex going on
all that turbulence will be inefficient for a lawn mower.
Watch a blender do its work, now imagine it trying to eject grass.
And if you isolate the blades, i imagine it would be hard to get overlap and not leave an unmowed stripe.
Not to mention all the extra expense to make it counter rotated, when same rotation is simple and cheap to do with just 1 engine, 1 belt, no gears etc.
I think most engines probably turn clockwise as viewed from the front. Marine applications with dual engines will have one of each.
The Vedeneyev M14P runs counterclockwise, opposite the vast majority of American-made aircraft engines.
There are a couple specific American-made aircraft engine variants that rotate counterclockwise, for specific twin-engine aircraft installations. They are rare, though, since most American light twins have same-rotation engines.
Oil and cooling need to be independent or reversable. Intake needs to be as cylinder is expanding, not blowing – that requires independent or reversable valving. And on a spark engine, the spark normally comes just before top dead centre, not just after.
So I’ve got a 10cc model-arcraft two-stroke diesel engine that can run either way.
Funny, when I look at my engine from the other end, it turns in the opposite direction.
You should see what happens if you take it south of the equator.
A two-stroke engine can be reversed, and AIUI sometimes it’s possible to accidentally start them in the wrong direction: you pull the cord (or stomp the kickstarter lever), and maybe you don’t develop enough momentum to spin the engine through TDC before ignition/combustion overcomes that pressure and causes it to start spinning in the opposite direction.
A four-stroke engine can spin in the reverse direction, but it can’t run in reverse because it pumps air in wrong direction. In the forward direction, the exhaust valve is open during an up-stroke of the piston, and the intake valve is open during a down-stroke - but when you reverse the rotation, the exhaust valve is open during a down-stroke and the intake valve is open during an up-stroke, so you’ll be pumping air out of the exhaust and into the intake. If your engine is port-injected or carbureted, you’ll never get any fuel into the combustion chamber; if it’s direct-injected (assuming the ECM is still willing to inject fuel), then the fuel will be injected late in a down-stroke before being pumped upstream into the intake manifold.
If you want to run a four-stroke engine backwards, you need (at a minimum) a specially made camshaft to open the valves at the right time. You’ll also need to change the spark timing so that it happens before TDC, just like it did when you were running the engine in the other direction.
If you have oil/coolant/fuel pumps, these will also need to be configured to rotate in the correct direction, lest the engine be starved of those fluids. Small engines (e.g. on lawn mowers) often don’t have any of those; they are typically carbureted (with the tank above the carb for gravity feed), air-cooled, and splash-lubed.
As noted upthread, some engines are designed/built in two versions with opposite rotation, intended to serve in pairs for marine/aviation applications. With left/right engines spinning in opposite directions, their torques on the water/air (and therefore their torques on the boat/airplane) cancel each other out, allowing for straight cruising across all power levels/speeds/attitudes without constant trimming of control surfaces.
The old “Scorpion” custom rear-engined Corvette used a Chevy engine with a custom camshaft that allowed the engine to run in the wrong direction–necessary because of the rear-engined design.
note that while crankcase-scavenged two strokes can run either direction, but usually don’t run well in reverse. A piston-ported (typical of chainsaws/weed-eaters) or reed-valve (high performance moto/kart) 2-stroke can physically run well in either direction with a simple change to the magneto to correct the spark timing.
timed-inlet engines (disc or drum rotary valve) might start in the wrong direction, but since inlet timing is wrong they won’t make any power if they do.
externally-scavenged two strokes aren’t inherently reversible. cam timing will be off, and the scavenging pump/blower will be spinning in the wrong direction. Interestingly, one of the more common on-road two strokes (the old Detroit Diesels from the '30s up through the '90s) were designed with this flexibility. if you wanted a reverse-rotation engine, you swapped the bellhousing and accessory drives from one end of the engine to the other, drove the blower from the opposite end, and voila! here’s a photo of a marine twin 6-71 Detroit setup:
the engines are basically mirror images of each other.
I think simplest way for a 4 stroke to be reversible on the fly is to not use a cam, instead use electromagnetic or pneumatic valves, like freevalve for example.
Oil could be either via electric pump, or engine driven piston type.
Water can be moved to electric.
Also need a reversible starter.
Just dont reverse rotate your lambo in the middle of the freeway.
which is dumb, because nobody is asking for a “reversible-on-the-fly” engine.
and proponents of the whole electromagnetic or pneumatic valve things are missing a key function of a camshaft. the camshaft doesn’t simply open the valves, it also provides a profile for the valves to follow on closing such that the valve head soft lands on the valve seat. You can’t just fire the valves open and let them snap closed, the valve heads would break off in short order.
Reversible ‘on the fly’ marine diesel engines are and have been the rule in merchant ship propulsion plants since diesels were introduced. On the 90% or so of merchant ships that have low speed diesels directly connected to fixed pitch propellers, that’s the only way to go backwards: you reverse the rotation of the engine.
That’s become simpler since the tendency of recent decades is for pumps (coolant, oil, fuel) and the scavenging blower of two strokes to be driven by electric motors, so they just keep rotating in the same direction driven by those motors. Likewise most of the scavenging is from the turbocharger which likewise needn’t reverse. And in more recent years the fuel injectors and exhaust valves of big low speed two-strokes are indeed controlled electronically rather than having a mechanical camshaft.
But direct reversing large marine diesels were still the rule in the days of mechanical camshafts and even with auxiliaries driven off the engine. You just had to have an admittedly somewhat Rube Goldberg arrangement of physically shifting the camshaft (either rotating it or sliding in a different set of cams depending on the engine type) and rearranging the input/output of the pumps and blowers for the engine to reverse. But it certainly works, two stroke or four stroke.
Machine Elf made the point about 2 strokes running backwards. I’ve seen dead engine starts in desert racing where occasionally a guy would kick his bike started when the banner dropped, only to have the bike shoot backwards when the clutch was dropped. Helluva surprise!
Um i do believe we were kind of talking about it, and it is in vein of what the OP asked about.
You do realize these are already in use on ships right? BIG ships Camless diesels with servo activated valves and reversible crank rotation
And of course there are poppet valves, those have been around forever
There is the Freevalve engine
And there is the desmodromic valve train, which has been used for quite a while, which literally and solidly slams the valves down and forcefully holds them shut with the cam.
If you want to pop a valve head off, mis-adjusting that system is the way to go.
And honestly, at 7000 rpms, do you think the valve lands very softly?
Sure, but camless four-stroke engines are extremely rare.
In a properly adjusted valvetrain, the cam profile sets the valve down more gently than if the valve came down ballistically. Take a look at any plot of valve lift versus crankshaft angle, and you can see that as the valve gets close to being completely shut, the cam lobe slows it down for a relatively gentle touchdown. On engines without hydraulic lifters (this is most motorcycles) you can screw this up by having excessive clearances in the valvetrain; then your valves will click-click-click, even at idle. If they’re really sloppy, then when you rev your crotchrocket up to 14,000 RPM, it’s a lot of extra stress on those valves to be slamming shut so hard; it makes the difference between the engine lasting 100,000+ miles or blowing up at 15,000 miles.
F1 cars use a pneumatic system for valve control. The system doesn’t merely open and close the valve as you would only be able to have it fully open for a very narrow amount of time. The valve gradually opens and gradually closes with piston movement. I think Peugeot even experimented with hydraulic system but they opted to go with pneumatic.
Just learned about the desmodromic! Wouldn’t be surprised if other high RPM engines use the same system, like in Ferarri, etc. Which would explain the required periodic maintenance intervals. As long as you maintain it, like with anything else, the engine should live long and prosper.
I’ll have to look into marine engine system, to see if the engine rotation can be reversed. That might have been the way, but, something tells me not so much anymore.
As, with anything that one designs, its a give a take process. If you want to design for: efficiency, power, reliability, reversibility, or cost; somethings have to give. It just seems overly complex to have an engine that can be reversed on the fly, for starters, the whole system needs, drive to engine, to come to a dead stop. Probably locked, and then the process to reverse begins. It seems that the use of smaller auxiliary units mounted within the hull could do the same. I believe cruise ships do that, they have electrical thrusters mounted that are perpendicular to the normal way of travel to push the ship sideways.
There were kits in the late 1970s for reversing Ford Pinto engines. Cam and starter plus some other stuff. The idea was to bolt it onto a VW chassis. My buddy did this on a convertible, and it did kick around pretty good.
More detail here:
It’s a long-standing tradition that is still used on Ducati motorcycles (just like BMW continues to make bikes with boxer engines), but it’s expensive and maintenance-intensive, and with modern design and manufacturing methods, high-RPM valvetrains can be (and usually are) made without it.