Amusing tale from the engine dyno cell

[Chris Wilson]

I read the following last night, by Tom Sharp. No, not THAT Tom Sharp of books about eccentric Englishmen fame, this one:

 

Tom is a consultant mechanical engineer specializing in the design and analysis of four stroke racing engines, through his company TSMD Ltd. Tom has over a decade of race engine design experience, and has operated as an independent consultant since 2005.

Since graduating with a 1st Class Honours Degree from Warwick University Tom has consistently worked at the highest level of professional motorsport; projects include Formula 1, Le Mans Prototypes, the WRC and BTCC to name a few.

 

 

 

 

DYNAMOMETERS

 

 

WHEN TO HIT THE RED BUTTON!

 

http://www.ret-monitor.com/articles/wp-content/uploads/2009/10/dynamometers-4.jpgThe author well remembers the first time he was given sole charge of overseeing the running in of an engine on the dynamometer of an un-named race engine manufacturer.

The engine in question was the first ever example of a Le Mans Prototype V8 and the author’s role was to do nothing other than warm the engine up on a base map which would be followed by a check over before the real mapping work commenced.

For around five minutes (no-one ever went through the data in much detail) everything went smoothly and nothing of any note happened; the engine hummed away and the hustle and bustle of the workshop continued apace in the background.

The world was a peaceful place and a lot of idling away was done, and as the author contemplated deeply exactly what was happening inside the engine, the engine built up temperature.

Then without any warning whatsoever the revs started to rise dramatically as if the engine had gone to full throttle. The engine continued to pick up speed and it was instantly obvious that is was in danger of over-revving and over-revving quickly; the author didn’t know exactly on the day (and still doesn’t actually!) how the rev cut strategy worked on that particular ECU.

A quick look at the throttle lever (this was well in the days of throttle cables) confirmed that it hadn’t moved and so there was only one thing for it.

As any dyno man will tell you there is only one reaction you can have in any unexpected circumstances; you find the big red button and you hit it!

The author did so and the engine died instantly. The soundproofing, being what it was in the day, meant that the regular dyno operator (along with most of the workshop) heard what had happened and came running.

Subsequent analysis of the data showed that the engine had over-revved but not to a point where anything had been damaged and after a borescope was deemed OK to continue. The data also confirmed that the throttle had not been opened.

Ten minutes later investigation of the dyno cell revealed the cause of the near disaster; an hydraulic oil return line from the dyno controller had come adrift, allowing the fluid to drain away until control was lost, which caused the dyno to lose all load during running. With no load on, a 4.0-litre V8 will happily spin up even on idle.

So the main lesson learned that day was the fact that anything can and at some point will go wrong.

Nowadays the world is a different place and a test cell can be rigged up such that an engine is automatically cut in the event of a problem but that is not always the case.

So if the author has one piece of advice for you; always know where your red button is!

 

 

It reminds me of a time when I was on the phone to Brian Hart's and someone asked me to hang on, they couldn't hear as an engine was on the dyno. Happy to listen for a few moments to what sounded like an F1 in full song I was rather shocked by the wail terminating in what, even over the phone, was a dreadfully big bang and total silence, save for someone shouting a few choice expletives, and the bloke coming back and saying sorry to keep you, but we have just had a bit of an expensive whoopsie in the dyno room. I can't see what's happened until the smoke and steam clears and the flames have been extinguished, but its definitely not going to make Brian's day.........

[Matt H]

I know where my red button is oin my Auto

[caseys]

I bet working with a dyno is actually quite a fun and interesting job.

 

We have big red buttons on numerous kit in our field of work. Normally accompanied by a white button which you use in 'normal situations'.

 

I asked some engineers what sort of situations I should actually use the Big Red Button (BRB) for, as in fact in some kit it's literally a kill switch, physically slicing power feeds on some items.

 

The response?

 

"Only when it's on fire"

 

Considering some places had a Halon extinguishing system in place for fire suppression (now restricted to military uses only) which had 1000L cylinders against the wall with a pressure well in excess of 20 bar the last thing on my mind was the BRB. Halon whilst not fatal in most cases does contain acid which can eat away your eyeballs..

[pedrosixfour]

But surely even a race engine experiences a no-load situation when sitting in the pits during a tyre change or on the starting grid?

 

How are the revs kept in check or "idling" then?

[Chris Wilson]

It would have been under a fairly light load from the dyno, so when the hydraulic line failed and that load was removed, the revs would go through the roof. It wasn't just revving slowly at no load, as in a pit stop. Race engines often only need a whiff of throttle on no load to go beyond their rev limit.

[pedrosixfour]

So a similar situation to driving along in a high gear at a steady rate then pressing the clutch pedal without removing your right foot from the accelerator pedal and the apparently stable revs shoot up.

 

Makes sense now. Sorry for being a pleb Chris.