OT: Why can't a petrol engine start itself?

Wouldn't it be possible to design a petrol engine so whichever piston is in the right position gets an injection of fuel and air mix and a spark and stars the engine rotating, without the need for a starter motor? Especially 8 cylinder engines, surely one is always in the right position to get it going?
--
If Christians want us to believe in a Redeemer, let them act redeemed. -- Voltaire

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thursday, March 22, 2018 at 4:41:34 PM UTC-4, James Wilkinson Sword wrot e:

in the right position gets an injection of fuel and air mix and a spark and stars the engine rotating, without the need for a starter motor? Especial ly 8 cylinder engines, surely one is always in the right position to get it going?

Voltaire
How are you going to get that injection of air? The air gets pulled in on the intake stroke, then compressed. The compressed air isn't going to stay there forever, the rings and valves don't seal perfectly. Plus one cylinder firing probably isn't going to generate enough momentum in the engine to compress the next cylinder.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 22 Mar 2018 20:41:30 -0000, "James Wilkinson Sword"
You still need compression. They do have airplane engines that start with a cartridge like a shotgun blank tho.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

If I blow air and petrol vapour into a tin can then drop in a match, it'll blow up. I don't need to squash it do I?
--
I was on a Southwest flight once that was delayed at the gate after everyone boarded. The flight attendant said over the intercom, "We're sorry for the delay. The machine that normally rips the handles off your luggage is broken, so we're having to do it by hand. We should be finished and on our way shortly."

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

As trader already mentioned, a single cylinder firing most likely wouldn't be enough to get the ball rolling. Maybe if it had already recently run and was still nice and toasty warm and you had a great shot of fresh air/fuel into the combustion chamber. You might (doubtful) get it to start and run from a single initial hit, then.
That's assuming you had some way of keeping the fuel air mixture and compression up on the cylinder you're going to try and start with. For all that effort on a seriously doubtful succesful start, might as well use the trusty electric starter. It'll either start your engine, or, run your battery down trying!
--
Don't become the next David Brooks cyberstalking victim!
Visit https://tekrider.net/pages/david-brooks-stalker.php (10/10 WOT)
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

In the early days of high powered electronic ignition there were reports of fords, being shut off warm and the key then turnrd on, starting from someone slamming the hood. ONE spark and away it went.
Would need a good flywheel.
I often "bumpstart" my ranger - slow walking speed in reverse - just let the clutch out for half a second - definitely less than 1/2 turn of the engine and it comes to like (with 159000km on it)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Not sure what "ignition" means on a diesel engine, but when I were a lad, our school bus would keep running if you turned it off and removed the key. You had to press the "stop" button to stop it running.
--
If you are going to try cross-country skiing, start with a small country.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 3/22/2018 8:24 PM, James Wilkinson Sword wrote:

Some have glow plugs to start them but compression generates the heat to ignite the fuel, this you no longer need the key. The shut off restricts air flow to stop it.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

So what happens on a normal car? Does switching off the ignition automatically shut off the air?
--
"The only time you have too much fuel is when you're on fire."

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 3/22/18 8:19 PM, James Wilkinson Sword wrote:

No. It shuts off the electricity to the ignition system. That eventually stops the power to the spark plugs. Video here: <
https://www.youtube.com/watch?v
udCm7DMzU>
The moderator talks funny.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 22 Mar 2018 20:34:13 -0500, Dean Hoffman

On today's engines the key shuts off the ignition AND the fuel. Virtually immediately.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Idling too fast and or a vacuum leak or running too hot (late timing) on a rocket and you can almosrt DRIVE it with the spark shut off - particularly on regular gas. Didn't need much carbon
Had a 1275 Stage 3 cooper engine in a Moke at the school in Zambia that WOULD drive into the shop with the spark shut off - if you feathered the clutch and didn't stall it. Over 15:1 CR and 81 octane gas - - - On 100 octane AvGas or race fuel it was apparently SCARY!! Couldn't buy good enough gas inthe country to run it after independence
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I had a petrol engined Renault Espace that would do that. The carburetttor was fucked and it often flooded itself, hence there was loads of spare fuel hanging around. Easy enough to stop. Place in gear, then let out the clutch with the brakes on.
--
A man spoke frantically into the phone, "My wife is pregnant and her contractions are only two minutes apart!"
"Is this her first child?" the doctor asked.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

He talks in correct English. No accent whatsoever. No stretching vowels like the yanks do.
--
The world's largest fruit are giant pumpkins. The world record is 1061lbs (481.3 kg).

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Dean Hoffman posted for all of us...

ed

to

In the early days of emission engines when the systems were mechanical ther e would be a condition called 'run on' when the ignition was shut off. It sounded like a mechanical coughing fit. Some cars had to be in gear to stop it. Clare can explain better than me.
--
Tekkie

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

te:

e a

emoved

eat to

there

t
stop

I had that with my 1988 Range Rover which had been badly converted to use petrol or LPG by the previous owner. It was also impossible to start it on petrol, even though that was what you were meant to do. It only started on LPG, after several tries, often with an explosion in the exhaust, which scared the shit out of anyone stood behind it.
-- If debugging is the process of removing software bugs, then programming must be the process of putting them in.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 03/22/2018 07:19 PM, James Wilkinson Sword wrote:

No, it turns off the ignition. No spark, no bang, no go. With a diesel you need to cut the fuel or the air. In most cases cutting off the fuel is easier than trying to block the air inlet.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload


The majority of the ones I've had turn off the electrical power to the ignition coil as well the electric fuel pump. I've had a couple of much older ones that didn't use an electric fuel pump. In those cases, I believe it was just cutting power to the coil.
--
Don't become the next David Brooks cyberstalking victim!
Visit https://tekrider.net/pages/david-brooks-stalker.php (10/10 WOT)
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Virtually every car since the early nineties has been fuel injected - which basically requires an electric fuel pump - and electricity to open the injectors. The key shuts off both along with the ignition.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload


Ayep. As I said though, I had a couple that didn't have electric fuel pumps.
--
Don't become the next David Brooks cyberstalking victim!
Visit https://tekrider.net/pages/david-brooks-stalker.php (10/10
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Site Timeline

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.