RichardS
N/A
I could argue that the starter motor is part of the ignition process of both a petrol and a diesel engine and therefore calling the key which operates the starter motor an "ignition key" seems perfectly logical.
Richard
Running engine (diesel) with the ignition turned off
- Thread starter Robert Wilson
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Richard
Beneteau381
Well-known member
BUT they do have compression ignition! So the key switch could rightfully be called an ignition switch! After all we dont differentiate by calling petrol engine ignition switches electrical ignition switches?
Beneteau381
Well-known member
Beat me to it!I could argue that the starter motor is part of the ignition process of both a petrol and a diesel engine and therefore calling the key which operates the starter motor an "ignition key" seems perfectly logical.
Richard
Quite rightly called an ign switch, turn it and it puts in place a system of events that causes ignition of the engine! Doesnt matter whether its a diesel or petrol one, both serve the same purpose!
JumbleDuck
Well-known member
Since this thread has descended to pedantry, I am strongly attracted to it ...
"Ignition" does not have to include electrical systems. A match ignites a fire, just as frictional heating ignites the match. The definitive (and highly readable) work on rocket fuels is "Ignition" by John Clark, and most of the fuels he worked with were hypergolic - they ignited on contact without even heat required.
While I am at it, small marine diesels do not ignite the fuel by compressing it. They ignite it by squirting it into hot air.
"Ignition" does not have to include electrical systems. A match ignites a fire, just as frictional heating ignites the match. The definitive (and highly readable) work on rocket fuels is "Ignition" by John Clark, and most of the fuels he worked with were hypergolic - they ignited on contact without even heat required.
While I am at it, small marine diesels do not ignite the fuel by compressing it. They ignite it by squirting it into hot air.
Stemar
Well-known member
All of which is why I use inverted commas around ignition when referring to the switch in question.
Winning pedant
rogerthebodger
Well-known member
Me too
Very true but diesel engines are called compression ignition engines.
It's the compressing the air that causes the heat to ignite the fuel being squirted into the now hot cylinder air.
JumbleDuck
Well-known member
I'm an academic. Petty, nit-picking pedantry is what I do.Winning pedant
Of course, but it's surprising how many people think that full-size diesels work like model aircraft engines which really do squeeze a fuel-air mixture until it goes bang. Not losing you with the technical terms, I hope.
rogerthebodger
Well-known member
No Not at all not with Engines any way as I used to tune them in the late 1960's. I also like you I have a number of classic cars.
Some of the stress analysis I have not done for over 30 years so am very rusty on the details now , even through My undergrad project was using early finite analysis using data input on punch tape and ran on the science research council mainframe computer at Didcot in 1970/71.
I changed direction in the mid 980's as people would pay me money to fix and program the new fangled PC's Ended up writing applications on PC's to perform simple machine control functions, my first love. but if was applications like point of sale (Cash register replacement) and customs duty calculation and documentation where I made better money that Engineering.
Your location is SW Scotland, my dad was from Clyde Bank and worked at John Brown shipyard. Is this anywhere near you
PaulRainbow
Well-known member
If there is no ignition, how do they work ?
What happens to all the diesel that goes in ?
If it doesn't get ignited, surely there is no point in putting it in ?
RichardS
N/A
My model diesel engines had a variable compression ratio which was really useful for ignition and fine tuning. It's a pity that full-size diesels are less advanced in design.
Richard
alan_d
Well-known member
Except that, referring back to the start of this thread, if you turn off the ignition switch on a petrol engine, the ignition process (and the engine) stops. Turning off the "ignition" switch on a diesel does not (generally) have the same effect.I could argue that the starter motor is part of the ignition process of both a petrol and a diesel engine and therefore calling the key which operates the starter motor an "ignition key" seems perfectly logical.
Richard
PaulRainbow
Well-known member
Not strictly true. Most diesels (trucks, vans, cars, buses, etc) stop when you turn the "key switch" to the off position. Boat engines are different, because the stop solenoid has to be energised to stop the engine, not to allow the engine to run. See paragraph 1, post #14
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convey
N/A
It is combusted ... well, between some to most of it depending, as the plumes of black smoke they kick out testifies ... but by heat caused by compression. They operate as a much higher compression ratio than petrol engines. Some have glow plugs, heated by electricity, to give the initial heat boost to do so. old, elementary ones don't you just crank them up until they are going fast enough to generate enough themselves, and to stop them you can flip the decompressor lever. Some manual (cable), some solenoid operated.
Think of when you pumped up a bicycle pump as a kid holding the end, and they rapidly became hot (when a gas is compressed its temperature increases).
A diesel might have a compression ratios of between 15 to 23, while a petrol engine is between 8 to 10.
Petrol autoignites around 280°C, Diesel around 210 °C.
My only criticism of this video is that it shows the cylinderhead to have a hemispherical shape, which would reduce compression, when most diesels would have a flat top piston, meeting a flat cylinderhead, which would increase compression. Notice how the pistons have indentations in the centre where the fuel/air mix would be compressed into and squirl to ensure a good mix and atomisation. The lip around the edge 'squishing' it in as it meets the flat face of the cylinder head.
RichardS
N/A
As Paul says, 99% of diesel engines in the world stop when you turn off the ignition key so I would say that "generally" diesel engine keys are exactly the same in effect as petrol engine keys.
Richard
RichardS
N/A
Can I just make a general point here to help relative newcomers to the forum ..... when you see posters on this forum who have thousands of posts, it's probably best to assume that quoting them before typing long posts explaining how diesel or petrol engines work is somewhat superfluous to requirements.
Richard
Richard
convey
N/A
Does he know? It didn't show by his post.
There's no ignition switch or otherwise on a diesel. There may be a key and a barrel lock, but it performs some other purpose.
There's no ignition switch or otherwise on a diesel. There may be a key and a barrel lock, but it performs some other purpose.
rogerthebodger
Well-known member
There are also mainly 2 different types of diesel engine.
Common rail which have an electrically operated injector
Or
Pressure operated injectors
With an engine of the latter type the engine stops by stopping the fuel being pumped to the injector.
This is normally by either a solenoid either opening or closing off the fuel flow. A closing is by energising an solenoid to close the fuel flow or by energising a solenoid to allow a fuel flow. Th former is the cheaper one as you don't need a continuous rated solenoid where with the energize to run solenoid must be able to the energized all the time the engine is running.
With the common rail all that needs to be operated is to stop the electrical pulses to the electrically operated injector which i very much a kin to stopping the spark of a petrol. The "ignition switch will cut the electrical supply to the injectors thus stopping the combustion as in a petrol engine.
So the ignition switch does directly stop the engine.
A third type is the semi diesel that has a hot plate or glow plug that raises the temperature in the cylinder to a point where the diesel will ignite with reduced compression. This is some times just used to aid starting and not so much now as a normal running operation.
Common rail which have an electrically operated injector
Or
Pressure operated injectors
With an engine of the latter type the engine stops by stopping the fuel being pumped to the injector.
This is normally by either a solenoid either opening or closing off the fuel flow. A closing is by energising an solenoid to close the fuel flow or by energising a solenoid to allow a fuel flow. Th former is the cheaper one as you don't need a continuous rated solenoid where with the energize to run solenoid must be able to the energized all the time the engine is running.
With the common rail all that needs to be operated is to stop the electrical pulses to the electrically operated injector which i very much a kin to stopping the spark of a petrol. The "ignition switch will cut the electrical supply to the injectors thus stopping the combustion as in a petrol engine.
So the ignition switch does directly stop the engine.
A third type is the semi diesel that has a hot plate or glow plug that raises the temperature in the cylinder to a point where the diesel will ignite with reduced compression. This is some times just used to aid starting and not so much now as a normal running operation.
penberth3
Well-known member
I think some irony was involved in the post you quoted. You obviously missed it.
JumbleDuck
Well-known member
There was a Ricardo variable compression ratio engine in the thermo lab when I did my undergraduate degree. I think it was a diesel, but can't be sure. I was allocated a Ford petrol engine at the other end of the room.My model diesel engines had a variable compression ratio which was really useful for ignition and fine tuning. It's a pity that full-size diesels are less advanced in design.
RichardS
N/A
Paul Rainbow has over 9000 posts. He's forgotten more about diesel engines than most people will ever know, which gives him the right to be somewhat tongue in cheek.
Read the thread if you want the answer to your second paragraph.
Richard
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