Smoke/emissions testing for diesels

[Sputnik II]

I took the Diesel for the mot yesterday at a local garage and when they did the emissions test they just held the throttle to the floor until either the rev limiter cut in or valve bounce occured. Personally I don't think this is either necessary or the correct way of doing it. In the past when I've took the car to the Ministrys own testing stations they rarely rev them past 4000rpm and on one occasion the ministry tester told me off for over revving the engine.
Does anyone know the correct proceedure they should use apart from the ' test it to destruction' method ?

 

[Sputnik II]

wide open throttle is the correct procedure, if you dont like it then tough, your car wont get an MOT

If this is the correct procedure, then why don't the VOSA run testing stations do it that way?

 

[Sputnik II]

Do thet do the same for petrol engines?

Unless things have changed a great deal since I was in the motor trade, Petrol cars have their emmisions checked at idle speed and normal running temperature. They might rev them slightly just to clear them before or during the emmisions is checked.
I'm not clear on the Diesel test because the firm I worked for back then only worked on petrol vehicles.

 

[Sputnik II]

I don't have a problem with the car being driven hard but, to hold it with the throttle full open and no load on the engine is neither sensible or healthy to the engine IMHO.
The other thing is its not really a true reflection on the cars emissions in normal driving because, in normal driving you never need to exceed 3000rpm.

 

[Sputnik II]

if running without load damages an engine how are some engines "bench run-in"?

Probably because they ain't held at 6000rpm +

that's nonsense.
in a Turbo Diesel the turbo won't come on song until approximately 2500RPM.
obviously the engine needs to be tested to see what emmisions are like at the higher end of the rev range.

Thats also nonsense because, the point of the turbo being 'on song' is dependant on the vehicle and its design etc. A nova turbo diesel comes on song at 3000rpm . A 16 litre truck engine would have a turbo spinning like a whirlwind at just 1000rpm.

 

[Sputnik II]

notice the word APPROXIMATELY in my post.
now let's address your reply shall we?
according to you there is no need to rev higher than 3000 RPM in a diesel car.
if that's correct,and you are also correct in your Nova TD example then can you explain why the manufacturer constructed a vehicle with a turbo that according to you would be un-necessary to use?

Erm, What I actually said is there is no need to rev MY car higher than 3000rpm because its passed the point of maximum torque produced. My car is normally aspirated so nothing exciting is gonna happen however hard its revved.
My point of comparing a Nova to a truck is that you can't generalise all diesel vehicles as being the same and having the same power bands.

 

[Sputnik II]

i've checked the thread and cannot see you mention maximum torque at all.
what you actually said was there was no need to rev beyond 3000 RPM in normal driving.

Yes, that is exactly what I said and for the reasons I later gave!

I'd disagree with this strongly and would add that you could even be doing your engine more harm than good by doing this.
revving so low could promote soot build up over time.

Oh right, I'll rev the heck outta my engine and reduce the fuel economy from now on just for you !

this may come as a surprise but the MOT test isn't setup around your use of a vehicle.

Oh, my really ?

you may not rev your car more than 2krpm above idle but everyone else in the western hemisphere does and as such the emission test needs to pickup on this.

I'd probably say 50% drive like me but, you tell me seeing as you seem to know everyone in the western hemisphere.

we were talking about cars until you dropped HGV motors into the mix,why not throw in marine diesels for good measure?

Because the last time I looked marine diesels didn't go along on a tarmac surface but, trucks do.

all car turbo diesels will indeed develop boost at roughly the same point in their rev range so yes you can generalise.hgv's are different in that they have a much lower rev range to give prolonged engine life and of course when you have upwards of ten litres of capacity then your engine can easily make enough waste gas to spin the turbine below 1500 RPM.

Actually some of the new variable boost turbo diesels get the turbo spinning at low engine rpm's

 

[Sputnik II]

Opening the throttle on a diesel engine only regulates how much fuel is injected , the only way to test it's emissions is to inject the maximum allowed into the engine & that is ONLY going to happen at full throttle hence a diesel smoke test has to be done at full throttle, Some basic checks are carried out before the test is done which include oil level, bringing the engine up to normal running temp but most importantly the cambelt history has to be taken into account, The presenter of any diesel car should be given a card at reception stating what happens during the smoke test & if there is any doubt or the presenter can't confirm the cambelt history the testing station can & will refuse to carry out the test.

For the record the engine is held on the governor for aprox 5 seconds , if the smoke reading is within the limits after this time the car passes & thats it, this is known as "Fast Pass" , If if fails then the test is carried out up to a maximum of 6 runs & a mean average is taken , more often than not the first test run can be quite high especially if the car only pootles around as there is a buildup of soot in the exhaust which needs to be cleared out.

Thanks for that, thats pretty much what I wanted to know.