Peak cylinder pressures

[adi69]

Hi,
After much research I'm trying to find a way of measuring peak cylinder pressures within a petrol turbo engine and how much pressure/force a cast conrod can take before bending.
I'm aware of Dave Baker and the general enquiries he's likely to be inundated with but wondered if anyone else could help with this.
My research so has included the Honda RA168E engine from the 1989 McLaren F1 car which produced 16mpa peak pressure (1.6 V6 turbo 2.5 bar)
Any help is much appreciated

[227bhp]

You have to invest in the equipment to do it, take it to someone who has it or run it through a simulation program if you have the relevant info for that engine to input. Unlikely you have that info if it's F1.

[anonymous-user]

Industry std:

AVL_IndiCom


If you have to ask how much, you probably can't afford it.......

[stevieturbo]

adi69 said:

Hi,
After much research I'm trying to find a way of measuring peak cylinder pressures within a petrol turbo engine and how much pressure/force a cast conrod can take before bending.
I'm aware of Dave Baker and the general enquiries he's likely to be inundated with but wondered if anyone else could help with this.
My research so has included the Honda RA168E engine from the 1989 McLaren F1 car which produced 16mpa peak pressure (1.6 V6 turbo 2.5 bar)
Any help is much appreciated

You're asking very open ended questions.

Finding peak cylinder pressure is easy, just expensive. But that is of less importance as to when that peak cylinder pressure is occurring within an engine cycle.
Plex do a combustion monitor system, but you're getting towards £10k or so.

https://www.plex-tuning.com/products/pca-2000-comb...

As for the rod.....how long is a piece of string ?

[HJG]

High performance automotive turbocharged, port injected petrol engines will see cylinder pressures of around 120 bar max.

Direct injected may be around 160 bar.

A connecting rod will survive a much higher cylinder pressure than this since this force travels down the axis of the rod and does not act to bend the rod. A rod will buckle however if it is loaded eccentrically (in reality there is always some eccentricity because the rod big end will not be 100% concentric to the crankpin), but the force required to buckle a rod is enormous and far higher than the operating cylinder pressure.

Rods will however bend and/or buckle very quickly if the engine is hydrolocked (cylinder full of coolant, oil or fuel).

[adi69]

Thanks for the input and info.

The fuel injection pressure and combustion pressures are different which I'm aware of.
Maybe it's speed/torque that's applied to the conrod that needs looking at rather than the initial combustion force.
I think I'll research conrod manufacturers and see if they can shed some light/data on the situation. A cast conrod will have to go through stress and load analysis before being passed for application. The big question is will anyone divulge said info

[GreenV8S]

adi69 said:

I'm trying to find a way of measuring peak cylinder pressures within a petrol turbo engine and how much pressure/force a cast conrod can take before bending.

I imagine it would be possible to install a pressure transducer and fast data logger to capture peak cylinder pressures on a specific engine, and I suppose it would be possible to build a fixture to crush a rod in a press and measure how much force it took. I'm wondering what use that information would be, though. Is there some specific problem you're trying to solve?

[anonymous-user]

Peak rod loads can often be tensile rather than compression, ie occur at high rpm and low cylinder pressure, for example where you lift off at peak rpm to shift gear.

Most "rod failures" occur because something else has gone wrong first, be that a bearing or piston pin nipping up, a rod bolt loosening, or a piston / bore failure (ie pre-ignition or det causes piston crown to expand and partially seize in bore) that then over loads the rod.

Determining the "strength" of an existing cast rod i best done in a tensile / compressive tester, or by carefully FEA.

[stevieturbo]

adi69 said:

Thanks for the input and info.

The fuel injection pressure and combustion pressures are different which I'm aware of.
Maybe it's speed/torque that's applied to the conrod that needs looking at rather than the initial combustion force.
I think I'll research conrod manufacturers and see if they can shed some light/data on the situation. A cast conrod will have to go through stress and load analysis before being passed for application. The big question is will anyone divulge said info

You seem to be talking round in circles without any realisation you're asking how long a piece of string is ?

[Inline__engine]

get a good 1D sim it will tell you pressure vs crank angle. then you need masses and do some kinematic and dynamic calcs to work out inertia loads and force vectors and then you can design / analyse your rod or whatever. you'll need material properties to do strength, stiffness and fatigue calculations. there are few good papers online in pdf format to guide you

i recommend ENGMOD4T its quite affordable for a 1D sim

Edited by Inline__engine on Saturday 3rd March 09:06

[GreenV8S]

GreenV8S said:

Is there some specific problem you're trying to solve?

For example, are you concerned that an increase in cylinder pressure might cause rod failure? That seems unlikely to me.

[jmcc500]

Not sure I understand the question, or what you’re trying to achieve. I can tell you that typical common rail diesel passenger cars were running up to about 160bar Pmax for some time, but we’re now headed above 200bar. As we go up we are moving to steel pistons, basically following the heavy duty diesel trends. I recall that modern HDD engines (eg truck engines of 12-16 litre capacity) are heading towards 230-250bar.

I don’t think an F1 engine would be that high, certainly not the old NA engines, but not sure about the modern turbo ones. Generally the old ones make power through speed rather than extreme peak pressure.

[stevieturbo]

jmcc500 said:

Not sure I understand the question, or what you’re trying to achieve. I can tell you that typical common rail diesel passenger cars were running up to about 160bar Pmax for some time, but we’re now headed above 200bar. As we go up we are moving to steel pistons, basically following the heavy duty diesel trends. I recall that modern HDD engines (eg truck engines of 12-16 litre capacity) are heading towards 230-250bar.

I don’t think an F1 engine would be that high, certainly not the old NA engines, but not sure about the modern turbo ones. Generally the old ones make power through speed rather than extreme peak pressure.

Steel pistons.....hmmmm

[Boosted LS1]

What engine uses a cast iron rod these days or is this something ancient from the 50'ies or earlier?

[stevieturbo]

It's all a bit of a mystery really.

[adi69]

stevieturbo said:

You seem to be talking round in circles without any realisation you're asking how long a piece of string is ?

There's always an answer. It's just whether the right question is asked. That's my experience.
A cast rod has its limitations. Torque and the load placed on the rod through initial acceleration seems to be more of the area of concern rather than peak cylinder pressures. You hopefully learn as you go.
A rod manufacturer has to have data to work with to ensure premature failure doesn't occur. When engines are modified either boundaries have to be respected or an endless pot of money is present. I'm trying to ask the questions as I don't have a pot of gold at the end of the 🌈

[GreenV8S]

adi69 said:

It's just whether the right question is asked.

Perhaps if you explained what you actually want to know, you might get a useful answer.

[Boosted LS1]

Op why are you asking about cast rods when afaik they're no longer being used in automotive applications?

[Megaflow]

stevieturbo said:

jmcc500 said:

Not sure I understand the question, or what you’re trying to achieve. I can tell you that typical common rail diesel passenger cars were running up to about 160bar Pmax for some time, but we’re now headed above 200bar. As we go up we are moving to steel pistons, basically following the heavy duty diesel trends. I recall that modern HDD engines (eg truck engines of 12-16 litre capacity) are heading towards 230-250bar.

I don’t think an F1 engine would be that high, certainly not the old NA engines, but not sure about the modern turbo ones. Generally the old ones make power through speed rather than extreme peak pressure.

Steel pistons.....hmmmm

Apologies if I have misunderstood your post, but yes they are a thing:

http://www.mahle.com/en/products-and-services/comm...

[stevieturbo]

Megaflow said:

Apologies if I have misunderstood your post, but yes they are a thing:

http://www.mahle.com/en/products-and-services/comm...

Certainly a new one on me !!