piston size 4

[jfoldbar]

hi all.
im new to this forum hope to learn from it.
i have a question i hope can be explained regarding engine piston size.

so i recently bought a new truck for my business. its an isuzu with a 5.2liter 4 cyl motor.
and i got thinking why are engine designers now making engines with larger fewer piston. 20 years ago a 5.2l motor would have been a v8. why is it now a 4cyl

thanks

 

[EdStainless]

At one time years ago there were engines that were 5l per cylinder.
Engine design is a real balancing act.
HP vs torque, specific fuel consumption vs emissions, flexibility vs peak performance, and so on.
5l engines have been built in everything from 4 cyl to 12 cyl.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[gruntguru]

I assume it is a Diesel engine. Diesel engine efficiency increases with cylinder displacement.

je suis charlie

 

[enginesrus]

My first thought is cost of manufacture, why add more parts? And like mentioned diesel different than gasoline engine.

 

[BrianPetersen]

Different design priorities. In a utility truck application, high efficiency and low cost are at the top of that list, and smoothness of operation and quick-revving characteristics are at the bottom of the list or not even on the list at all. A large displacement slow revving 4 cylinder diesel engine is going to be rough-running and with a really heavy flywheel. In your truck, it hardly matters.

 

[PJGD]

I used to have a Field-Marshall tractor. The Field-Marshall has a 5 liter single cylinder 2-stroke diesel engine with a large external flywheel. Look on Youtube and you will see examples. Starting the engine was, shall we say, exciting. It did not run to high crankshaft speeds, but it had tremendous percussion when it came up to an obstruction - it would beat it down.

PJGD

 

[malbeare]

I still have a field marshall and it is in the process of restoration . shot gun shell start or if you are game there is a large starting handle on the flywheel with a decompression valve that is held open by a cable attached to a small disk that runs in a thread on the flywheel and drops off after half a dozen turns so you hope that you are strong enough to get enough speed to get over compression when the disk drops. if it back fires then you break an arm . if it fires you hope that the handle disengages haha


A tidy mind not intelligent as it ignors the random opportunities of total chaos. Thats my excuse anyway
Malbeare

http://www.sixstroke.com

 

[RodRico]

Many manufacturers are now building "modular engines" in which they reuse a standard cylinder (bore, stroke, valves, etc.) in various engines. It appears Isuzu uses a common cylinder design across at least 4 engines (4 and six cylinders, both normally aspirated and turbocharged). As for why Isuzu chose a comparatively large standard cylinder, I can only speculate. Their commercial family of diesel engines all appear to be optimized for efficiency and durability rather than size, and fewer cylinders of larger bore with low piston speeds fit the bill.

 

[gruntguru]

"malbeare (Automotive)4 May 19 17:27
I still have a field marshall and it is in the process of restoration . shot gun shell start or if you are game there is a large starting handle on the flywheel with a decompression valve that is held open by a cable attached to a small disk that runs in a thread on the flywheel and drops off after half a dozen turns so you hope that you are strong enough to get enough speed to get over compression when the disk drops. if it back fires then you break an arm . if it fires you hope that the handle disengages haha"

This prompted me to go looking on You Tube. I ended up spending 30 fun minutes watching enthusiasts starting an assortment of ancient engines.

je suis charlie

 

[kjoiner]

A little off topic, but I enjoy watching the shotgun starters on old radial engines. I also like watching the videos with radial engines on test stands where some poor guy madly cranking an inertia starter. You have to wonder when the person handling the mixture and throttle doesn't get it quite right and the engine stalls, if the crank man is cursing him under his breath.


Kyle

 

[enginesrus]

When using an inertia starter on the old radial engines, you crank and build up the energy then remove the hand crank and pull the engagement handle / cable. And if the engagement solenoid is working you could run up to the cockpit and do it there.
Fun stuff on the R-1830's on DC3's.

 

[kjoiner]

Have you seen the inertia starter for the Citroen?

https://www.youtube.com/watch?v=RNijql5V7s4

Kyle

 

[JayMaechtlen]

+1 for Citroen!

Jay Maechtlen

http://www.laserpubs.com/techcomm

 

[Marquis]

Bigger cylinders are more efficient in both diesels AND petrols.

This is due to lower surface-to-volume ratio and therefore lower heat loss.

The effect of this is better BSFC. From my database and experience on a petrol when the cylinder size reaches about 500 ccs, you get good best point BSFC (an outstanding number might be 235 g/kwh- for a PFI engine running a 10.5-10.75:1 CR). As you get bigger than this- the benefits level off and you don't get much better. (this is why the new 2.7 litre 4 cylinder from GM makes little sense to me). A 300 cc cylinder of square bore and stroke would be lucky to attain a best point BSFC number of 270 g/kwh by comparison. Bear in mind that the larger your bore- and cylinder size in general- limits you in the realistic attainable compression ratio you can achieve- so you have to balance that.

Similarly a big bore engine with short stroke will have a poor surface to volume ratio and more heat loss, but the designer may have been prioritizing getting better high speed airflow.

http://www.auto-scape.com

Sideways To Victory!

 

[BigClive]

On the subject of odd ways to start a big radial plane engine - it was apparently not unheard of when the starter motor (or battery etc.) was not working to loosely connect a few tyre tubes to the restrained prop - stretch the tubes - then let the prop go. Some planes relied on this starting method for months when parts weren't available.
Which reminds me - one of the dramatic moments in "Flight of the Phoenix" was when Jimmy Stewart was using the last starting cartridge - if it didn't start they were stuck in the desert. They could have the "tyre tube" method - somebody would
have been aware of it.

 

[gruntguru]

Marquis (Automotive)21 May 19 18:43
"Bigger cylinders are more efficient in both diesels AND petrols. . . .
. . . . Bear in mind that the larger your bore - and cylinder size in general - limits you in the realistic attainable compression ratio you can achieve- so you have to balance that."

Do you see the contradiction? "Bigger" has a limit.

As SI cylinders get larger you reach a point where flame path gets too long and efficiency must suffer - unless you can provide multiple ignition points. This limit does bot apply to Diesels.

This is why large gas (vapour) engines use a form of jet ignition - special spark plugs with a pre-chamber and orifices. Mahle TJI is extending this tech to liquid fuelled SI engines which may see an extension in optimum cylinder size at some time in the future.

je suis charlie

 

[gruntguru]

Big Clive.
I would like to see the tyre tube method in action.

je suis charlie

 

[enginesrus]

Tire tube ? Probably not a bicycle tire tube. So what to tie it off to? We need pictures.
And what is the largest engine to start that way.

 

[BigClive]

The engine in question was on a DC-3/C-47 during the war. The 'plane had a non-operating starter motor on one engine and it was travelling around remote bases for a few weeks. The starting involved 4 or 5 tubes (presumably from aircraft or truck etc.) linked together with the end looped around the prop, stretched out by a group of blokes (4,5 20?). A restraining rope was tied from the prop to an immovable object (truck etc.?) The rope was cut, the engine spun over, starting and flinging off the tubes etc.
As it was WW2 I wasn't actually there (a little too unborn) but I see no reason to disbelieve the story. If one man can supply enough stored energy in an inertia/flywheel starter to start a big aero engine It seems quite feasible to me that a group 4 or 5 humans could store enough energy in the tyre tubes to easily start a P&W R-1830.

Another story I have read (if you didn't believe the above stop reading now) involved starting an F-86 again with a dodgey starter. Another F-86 was parked in front and blew its exhaust into the inoperative F-86's intake spinning over the engine and allowing it to be started.

This same article reported that an out-of-fuel F-86 at a non-jet base was refuelled with Avgas (instead of jet fuel) and apparently operated normally.

 

[Lou Scannon]

In the short term, gas turbine engines hardly care what fuel they burn, as long as it ignites and burns. In the long term, they may care about deposits left or corrosive attack by fuel or combustion constituents, on various parts of the system that is wetted by the fuel or its combustion products.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz