Engine starting and stopping.. 5

[cshmech]

I have a basic(silly!!) doubt about it.. When an ic engine(say 4 stroke) stops, it may stop at any position. When an engine is started, fuel supply and spark is given. But how its possible that it starts to run again in the same direction(CW-CCW)??
I mean, it should run in the same direction, but whats the mechanism which makes sure that engine runs in the same direction??

 

[Scirockett]

the starter turns the motor the way it's intended to run. for counter rotating engines say in a boat, you need one CW starter and one CCW starter. If you ever shutdown or lose ignition on a marine engine under load, chances are it will diesel (run on) and actually runs backwards. This can pull in water from the exhaust mani's which isn't nice either. probably tmi, but it's your starter that must spin the right direction to get the engine running.

 

[carnage1]

On modern motors the electric starter only turns one direction.
If you get old enough, like my family's 1910 Michigan, then the electric starter does not guarantee rotation direction. The starter works by filling the cylinders with an explosive gas, then you press the button and all 4 cylinders fire hopefully spinning the motor in the right direction and not melting a hole in a piston. Needless to say we use the hand crank to avoid the problems with the starting system.

Luck is a difficult thing to verify and therefore should be tested often. - Me

 

[GregLocock]

Incidentally, engines usually stop in the same approximate position each time.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Lou Scannon]

I'm struggling to come up with an actual 4 stroke engine that would be able to run the wrong direction. Take a conventional spark-ignited engine. It is a self powered pump. There is no source of chemical energy on the exhaust side, so running backward is not an option.
Now a direct injected engine, diesel or gasoline, doesn't depend on the pumping action for chemical energy, but I'm pretty sure no electronic engine is going to allow itself to run backward, even if it were capable. That leaves mechanical diesel engines. Well, they depend on mechanically driven mechanical pumps for their chemical energy. I'm going to go on a limb here and say in-line and distributor pumps are not going to be delivering fuel to the injectors when turning backwards. That leaves mechanical unit injectors. Hmmmn, it just might work! (injection timing would suck, though).

 

[cshmech]

Greg, what makes sure that the piston stops approx. in the same position. It has 50% probability to stop either on its way (upwards or downwards.. irrespective of the stroke). Suppose if it stops on its upward way motion, when its started again by an explosion, it wil run in the opposite direction to which it was running previously right?

Carnage1, id like to know more about your 1910 Michigan..

Im totally unaware of the starters and motors you guys are talking about. Please provide me with some links, so that i can understand deeply.... and we are talking about ic engines only right??

Thanks again for replying me friends..

 

[GregLocock]

Nothing 'makes sure' it stops in the same place, it is just the way the whole thing works.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[hydrae]

The diesel engines that run backward are 2 stroke super or turbo charged, they are used in ships to get a reverse gear without a gearbox.
they have two camshafts for optimal performance in each direction
when the skipper wishes to change direction, fuel feed is stopped, compressed air injected into the cylinders timed to reverse the direction of the crankshaft, meanwhile the camshaft is swapped, then fuel feed is restarted. If the fuel is restarted before the crankshaft changes direction, the engine will continue to run forward on the backward cam, but it runs very rough.

The super chargers or turbo chargers continue to run in the same direction while the engine runs in either direction



Hydrae

 

[ivymike]

what drives the supercharger?

 

[hydrae]

The ones I have known about were turbo, but an APU could drive the supercharger. Compressed air was also directed at the turbos for cold startup.
Hydrae

 

[SomptingGuy]

"what drives the supercharger?"

Easy, you just put a twist in the belt

- Steve

 

[cshmech]

That was little explaining Hemi.. thanx..
Ive voted for u.. lot many times..

Let us see guys if someone can come up with a better explanation.. So lets keep it going..

 

[SomptingGuy]

"I'm going to go on a limb here and say in-line and distributor pumps are not going to be delivering fuel to the injectors when turning backwards."

I think you are right. Althought the actual HP pumping elements don't know or care which way they are going, the supply pumps (I think DPA/DPC/DPS use vane pumps) are going be running the wrong way to work.

- Steve

 

[dgallup]

cshmech (Mechanical)
2 Oct 08 21:23
... when its started again by an explosion ...

What engines are started by an explosion? Everything I am familiar with has some form of electrical starter, air starter, kick starter, pull starter, spring starter or hand crank. None of these is going to start the engine in the reverse direction. I know of no four strokes that will run backwards.

Lots of 2 strokes will run backwards but the spark timing will be way late so they make very little power. Glow plug two strokes on the other hand will happily run backwards. Some of those are most easily started by turning them backwards & the first combustion event will reverse direction & make them run forward.

Engines almost always stop as they are coming up against a compression stroke. Almost never on an expansion stroke. Multi cylinder engines are less consistent as the forces are more nearly balanced.

 

[cshmech]

dgallup.. gr8 man.. Starred u..
You explained almost everything..

 

[Bribyk]

Mazda does have a new system that starts a small 4-stroke using an explosion, I believe on a direct-injection engine. Similar to the two-stroke in dgallup's post.

 

[hydrae]

In the movie “Flight of the Phoenix" the engine is started by what looks like shot gun cartridges inside a revolver barrel. The shot is fired, then a sound of a turbine whining, while the blade starts to spin, whether this is an exhaust poof depends when the bad guys are about to arrive.

Anyone know how that works?
Hydrae

 

[BrianPetersen]

Bombardier snowmobiles with their SDI electronically-controlled fuel-injected two-stroke engines go in reverse by reversing the rotation of the engine at a push of a button ...

When you press the button, it cuts fuel, then as the engine coasts down the ECU predicts the stroke at which the engine will fail to get over the next compression stroke, and gives that cylinder a squirt of fuel, then fires the spark plug the moment the engine comes to a stop on that compression stroke ... presto, the engine then runs backwards. Saves having to make a forward/reverse gearbox. Presumably this offsets some of the extra cost of the fuel injection and emission control apparatus.

But the normal starting mechanism is only capable of rotating the engine in the forward direction, as per standard practice.

 

[berkshire]

hydrae
That is a Kaufman or hot gas starter, an explosion from a cartridge is turned into a stream of hot gas to spin an engine up to speed for start. Lighter ,yes, more reliable , not always.
B.E.

 

[drwebb]

"Flight of the Phoenix" - I second the inquiry. Of course it works dramatically by building suspense whether the engines will start before they run out of cartridges. But how did it work mechanically??