Internal combustion engine.

[daryle]

OK this is probably stupid so apologies if so.
Always seemed to me that igniting a fuel air mixture when the piston is an almost vertical position is not good for producing power, can use powering a bicycle for instance, you use maximum force to push the pedal when it is well and truly on it's way down.
So could an engine be developed that would fire at say 20% after top dead centre?.
I understand that an enormous amount of compression would be lost but could this be rectified by the use of supercharging/turbo?
Surely this has been tried before, or maybe i am missing out on something completely basic.
Anyway if it is a stupid idea i may have given someone a laugh.
Cheers guys.

[Windsor220]

Compression is one reason. The other is piston speed as it the flame from the combustion would struggle to catch up with the downward moving piston

[Itsme]

You are talking engine timing, engine power is at best with advance ignition before TDC, if ignition at or after TDC which is retarded you loose power.
With supercharger/turbo will not make any difference imo.


Cheers.

[cheap]

Power, economy, meeting emissions, reliability and cost are all integrated. Road legal ICE engines are always a compromise. Ignition at BTDC at TDC or ATDC, opening of inlet, closing exhaust, overlap, everything has been tried - there is no magic pudding without impacting something else. FWIW each generation of ICE does improve upon the last.

[Raptor]

Just read this; https://en.m.wikipedia.org/wiki/Ignition_timing

Ignition after TDC is seriously retarded





.

[Craig@AUDI]

Originally Posted by Raptor

Ignition after TDC is seriously retarded

[jpd80]

[happy1]

Most things have been tried by now.
Here are some of the alternatives to 'standard' 4-stroke otto engine design, that have had some commercial use:

Atkinson cycle 'otto' engine:
https://en.wikipedia.org/wiki/Atkinson_cycle

Miller cycle:
https://en.wikipedia.org/wiki/Miller_cycle

Variable compression:
https://www.popularmechanics.com/car...ession-engine/

Variable valve lift to reduce pumping loss:
https://www.bimmerfest.com/news/1262...w-valvetronic/

I have no experience with the Atkinson and Miller cycles, and the variable compression engine is still very new.
I have experienced the great improvements on fuel efficiency the variable valve lift has offered since BMW started with it in year 2001. Not sure how many other manufacturers have done similar.

[jpd80]

Originally Posted by happy1

Most things have been tried by now.
Here are some of the alternatives to 'standard' 4-stroke otto engine design, that have had some commercial use:

Atkinson cycle 'otto' engine:
https://en.wikipedia.org/wiki/Atkinson_cycle

Miller cycle:
https://en.wikipedia.org/wiki/Miller_cycle

Variable compression:
https://www.popularmechanics.com/car...ession-engine/

Variable valve lift to reduce pumping loss:
https://www.bimmerfest.com/news/1262...w-valvetronic/

I have no experience with the Atkinson and Miller cycles, and the variable compression engine is still very new.
I have experienced the great improvements on fuel efficiency the variable valve lift has offered since BMW started with it in year 2001. Not sure how many other manufacturers have done similar.

Atkinson cycle is used mostly with Hybrids although Mazda's SkyActive could be deemed a version
using late intake closing to reduce pumping losses and it's generally higher compression

Miller cycle is more or less approximated by adding forced induction to Atkinson cycle,
Turbo DOHC engines that use VCT can delay intake valve closing to vary dynamic compression.

While OEMs may have focused on fuel efficiency, that need is also tied to the local cost of fuel
and I suspect that increasing vehicle weights due to better crash protection nullified that.
The other part of that is manufacturers like Ford and GM downsized engines, added turbos
and more gearbox ratios, basically kept fuel economy similar with a heavier body
and maybe more performance over the older models....

[Trevor 57]

So, what is an external combustion engine

[Vesper Martini]

The full affect of the air/fuel explosion does not occur a TDC. It progresses to fill the chamber to well past that 20% mark

skip to 3.35 in the video below
https://www.youtube.com/watch?v=xflY5uS-nnw

[Raptor]

Originally Posted by Trevor 57

So, what is an external combustion engine

[Vesper Martini]

Originally Posted by Raptor

image

no substitute for cubes Trev

[jpd80]

It will be interesting to see how long engines hang around, a race between
added efficiency from hybrids to efficient batteries eliminating on board ICEs.

As battery tech gets cheaper and cheaper, OPEC will feel the branch crack and
start dropping the price of oil just to keep sales going......

[simon varley]

if anyone is interested, this is by far the best text I have read on ICE

https://trove.nla.gov.au/work/12815604

[Trevor 57]

Well done Raptor. You win the prize. Not too many know that.

Every time I hear someone talk about internal combustion engine I ask the same question and more times than not I get no answer

[Trevor 57]

https://youtu.be/kA0E7kRhd6M

[Trevor 57]

https://youtu.be/EVxByLO_6cA

[Crazy Dazz]

Originally Posted by daryle

OK this is probably stupid so apologies if so.
Always seemed to me that igniting a fuel air mixture when the piston is an almost vertical position is not good for producing power, can use powering a bicycle for instance, you use maximum force to push the pedal when it is well and truly on it's way down.
So could an engine be developed that would fire at say 20% after top dead centre?.

Work is done by force over time, therefore need to maximise the amount of time there is force on the piston.

Furthermore the force is exerted by the pressure of the gas. That pressure continues until the exhaust valve is opened. So you're not "losing" pressure" by starting early.

[daryle]

Seems that all that initial energy is wasted because the piston is very close to being in a vertical position, be interesting to know when the expanding gas looses it's effective power value. Thinking maybe 1/2 way down/45%?
Old school here, still cannot get my head around modern engines running ??13/1 compression ratios when back in the day 11/1 was about as much as you could run.
Lol my old 351 falcon with basically a phase 3 engine build would have loved 13/1.

[happy1]

I read this in an article on Wikipedia:

'The ****el engine has problems in fuel efficiency and emissions when burning gasoline. The slowness of a gasoline mixture to ignite, its slowness in flame propagation speed and the quenching distance of 2mm to hydrogen's 0.6mm, results in the fuel mixture in the long moving combustion chamber not being fully burnt, wasting fuel that would have created power reducing efficiency. This unburnt fuel is ejected into the atmosphere via the exhaust pipe, giving emission problems. This is not a problem when using hydrogen fuel as all the fuel mixture in the combustion chamber is burnt, using all the fuel to create power, giving near zero emissions and raising fuel efficiency by 23%.'

Seems that if you use a faster burning fuel such as Hydrogen, you could delay your ignition point.
Anyway, the response by Crazy Dazz seems to be spot on: You are not 'loosing' any of the pressure by starting early, the gas mixture is very compressible, and it contains the energy as a compressed gas until it is allowed to expand.

[Vesper Martini]

Originally Posted by happy1

I read this in an article on Wikipedia:

'The ****el engine has problems in fuel efficiency and emissions when burning gasoline. The slowness of a gasoline mixture to ignite, its slowness in flame propagation speed and the quenching distance of 2mm to hydrogen's 0.6mm, results in the fuel mixture in the long moving combustion chamber not being fully burnt, wasting fuel that would have created power reducing efficiency. This unburnt fuel is ejected into the atmosphere via the exhaust pipe, giving emission problems. This is not a problem when using hydrogen fuel as all the fuel mixture in the combustion chamber is burnt, using all the fuel to create power, giving near zero emissions and raising fuel efficiency by 23%.'

Seems that if you use a faster burning fuel such as Hydrogen, you could delay your ignition point.
Anyway, the response by Crazy Dazz seems to be spot on: You are not 'loosing' any of the pressure by starting early, the gas mixture is very compressible, and it contains the energy as a compressed gas until it is allowed to expand.

I think the swear filter has removed ****el engine.
which would be a rotary they had a second (trailing) spark plug for the 2nd burn

Mazdas Hydrogen rotary engine
https://www.mazda.com/en/innovation/technology/env/hre/

who would have thought the rotary could be an environmental solution.

not sure where this is going now?

[b0son]

Originally Posted by daryle

OK this is probably stupid so apologies if so.
Always seemed to me that igniting a fuel air mixture when the piston is an almost vertical position is not good for producing power, can use powering a bicycle for instance, you use maximum force to push the pedal when it is well and truly on it's way down.

And yet for maximum cycling power, you stand on the pedals and use gravity to increase your vertical force... and that starts from TDC.

[Ford17]

Originally Posted by Bevsta007

I think the swear filter has removed ****el engine.
which would be a rotary they had a second (trailing) spark plug for the 2nd burn

Mazdas Hydrogen rotary engine
https://www.mazda.com/en/innovation/technology/env/hre/

who would have thought the rotary could be an environmental solution.

not sure where this is going now?

Mazda were running test hydrogen-powered rotary engines back in the 1980's.
Seems unfortunate it hasn't amounted to anything much bigger.

[yearby]

Originally Posted by b0son

And yet for maximum cycling power, you stand on the pedals and use gravity to increase your vertical force... and that starts from TDC.

err no!

The force applied to the crankshaft by the piston at TDC to induce a rotational force of the crankshaft equals Zero.

In other words, it does not matter how much force is applied to the piston, it will never induce rotation in the crankshaft @ TDC.

All that happens is the energy (combustion pressure) is stored until the crankshaft is a greater mechanical leverage point.

[yearby]

Originally Posted by Crazy Dazz

Work is done by force over time, therefore need to maximise the amount of time there is force on the piston.

Furthermore the force is exerted by the pressure of the gas. That pressure continues until the exhaust valve is opened. So you're not "losing" pressure" by starting early.

Work done is the force (applied on the piston) x the distance the piston travels.

Power is the work done divided by the time taken.

Therefore-

Power (of the piston on the downward stroke) = ((force on the piston)x(piston travel)) / time

If there is no travel of the piston, there is no power at that moment in time.

By starting ignition early, force is applied down on the piston when the mechanical advantage favours the reverse rotation of the crankshaft.

But it is a case of best fit, that is to find the best compromise for timing for the best power outcome.

[b0son]

Originally Posted by yearby

The force applied to the crankshaft by the piston at TDC to induce a rotational force of the crankshaft equals Zero.

And that would be relevant if the crankshaft was not already rotating. But OK, I will amend my point and say 'just after TDC'.

[mike_nofx]

Oh my god... this idea is genius!

How did engineers miss this concept over the last hundred years and hundreds of billions spent on engine development?

[Franco Cozzo]

Originally Posted by Raptor

image

We need nuclear powered trains

[aussiblue]

no substitute for cubes

Uncle Tony doesn't totally agree: https://www.youtube.com/watch?v=CuDtY2dBqjI