Safe Speed Forums

I was wondering, when they test a vehicle for emissions what to they do about the air intake?

From what I understand, an engine gets fuel and air in to the chamber, this gets ignited somehow which causes an explosion, then the contents of the chamber is pushed out of the exhaust.
So there are two inputs, fuel and air.
The explosion is basically fire, which I believe I remember reading needs fuel, heat and oxygen to exist.

As the air intake isn't pure oxygen and presumably contains some carbon dioxide (among other things) does this get taken into consideration?
Do they run the engine on pure oxygen for the tests?

In fact, why don't all vehicles run with a tank of pure oxygen? Wouldn't that make them better/faster/more efficient/more fun/more likely to explode...

Would it be worth measuring all of the energy outputs for a comparison between different engines? Kinetic energy (that's the one we want), heat, noise and exhaust gasses?

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Andrew.

This is a very good point.
acording to on of my little scince books the earths atmosphere is:
78% Nitrogen.
21%Oxygen.
1% Other gases about 0.04% Carbon dioxide.

however I suspect on a road or where there is loads of cars the concentration may be higher.

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Oct 11 Birmingham Half Marathon. I am running for the British Heart Foundation.
http://www.justgiving.com/Rob-Taylor

YUP!

Give it more oxygen (and more fuel in the right proportion) and it WILL go faster! You can either do this with a turbo (or supercharger) or by increasing the concentration of oxygen going in. The first way increases the amount of oxygen (and all the other stuff too). The second way just increases the amount of oxygen. Nitrous Oxide kits are the way to go if you want option 2. That increases the concentration of oxygen dramatically.

However, for emissions tests, they use atmospheric air because that's what the engines are supposed to run on. Interestingly, I've heard that in parts of the world with very poor air quality (like Los Angeles or Mexico City on a bad day) the most modern cars actually go around "cleaning up" the atmosphere - i.e. the air coming out of the tailpipe is cleaner than the stuff going into the air intake! Unfortunately, while they probably DO remove some pollutants, they still chuck out CO2 - which is (we're told) public enemy No. 1 these days!

Yeah, it seems the greenies are aiming to reduce CO2 output to nil, but don't hold your breath.

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Peter Humphries (and a green V8S)

Rather strangely, water vapour has a much greater greenhouse effect than CO2. So, the "most green looking" alternative at the moment is hydrogen fuel cells? Let me see

You burn fossil fuels (and so create much pollution) to generate electricity that you use to electrolyse water to produce hydrogen that you then burn to produce a more "greenhousey" waste than you would if you'd just burned the fossil fuel in an internal combustion engine

... and they call that green

Now, here's a thought The measures of pollution for the MOT are concentration of CO, concentration of unburned hydrocarbons, and concentration of particulates. There is a way to reduce all three massively with very little effort - just introduce lots of fresh air into the exhaust. Although the amount of CO, hydrocarbons, and particulates per mile is the same (or slightly more - because the energy to power the fresh air blower must come from somewhere), the concentration (i.e. amount per litre of gas coming from the exhaust) is reduced. AFAICT, that would be perfectly legal - crazy or what?

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Will

The blower wouldn't need to be particularly powerful either, and a solenoid could shut it off to make it one-wayt only - and it would only need to cut in at tickover

In fact it could be driven straight from the bottom pulley via a dog clutch - all in the engine bay and cost next to nothing. In fact a cost saving might be possible as you could eliminate all - or most - of the crap that gets mixture spot on for emission if you had a good expulsion fan supplementing things

The MOT also checks the "Lambda" value on a catalyst -equipped petrol car. This being a measure of how rich or weak it is running. An "air leak" in the exhaust can throw that value way out for the reason you describe.

I never knew water vapour was a greenhouse gas though?! What aren't any of the tree-huggers moaning about it? In fact, it's not even a gas really as far as I'm aware???

Yes, it's classed as a gas, 'coz it is...

It's also the major greenhouse gas... Without water vapour in the atmosphere the planet's average temperature would be some 35 degrees C colder, ie about -20! The reason the tree-huggers don't get too excited about it is that, because of precipitation, it remains in equilibrium (depending almost totally on the prevailing temperature) - so if there's a temporary increase in water vapour for some reason, it just rains a bit more and things are back "to normal" in a day or so... CO2 on the other hand, hangs around for ages before being either absorbed into the sea (making it fractionally more acid) or turned into trees - and is thus treated as a "forcing" (ghastly use of English!) for global warming. However, I'm very sceptical about the AGW CO2 "church" - planetary temperature seems to follow the sun rather closely, something that the IPCC seem somehow to have failed to notice in the excitement over their "hockey stick".

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"Politicians are the same the world over... We build bridges where there aren't any rivers." - Nikita Kruschev

My old M5 has something very like this called an 'auxiliary air pump'. It only runs for about 3 to 5 minutes when the engine is cold. The clutch is electrically operated by the ECU. It's hard to know exactly what it does, but I believe it injects fresh air into the exhaust manifold. It's definitiely somethng to do with 'emissions'.

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

Pure oxygen is not practical becaue of storage problems. Also it used 14 times more air by weight than it does fuel so you would need a HUGE tank.

All modern engines use an oxygen sensor in the exhaust to compensate so there should be no need to measure this. Atmospheric pressure is far more critical whuch is why most Dynos give "corrected" powe outluts which adjust for temperature and pressure (air density).

If you want to make sure you have optimised you car for the test make sure it has a brand new air cleaner. This will affect intake air density.

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Speed camera policy Kills

14 times more air, yes. But since air is only 20% oxygen the ratio of oxygen to fuel would be about 3:1.

Not that I'm suggesting it's a good idea.

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

Nitrous Oxide is the favorite way to boost oxygen content at atmospheric pressure. It can be injected in a liquid state so you get a massive volume of oxygen going in. It also helps to control combustion so you get a "burn" not "detonation".

I forgot to mention that when an engine is "mapped" by the manufacturer they account for all possible environmental conditions from -40 to +50 ambient and air pressure up to 10,000 feet altitude. The oxygen sensor provides a closed loop control varifying that the map is giving the correct mixture control. So basical whatever the conditions at the time of your MOT the engine management system should optimise the emissions.

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Speed camera policy Kills

Certainly not, don't make it too easy for the buggers to tax it!

Does your Beamer have a cat? If so, it might be something to dump air into the exhaust to provide a bit of extra oxygen to help the cat "light up" to operating temperature quickly. I've seen air injection on many older USA engines but I thought it ran continuously to help the cat "burn" off excess unburnt fuel and carbon monoxide.

Ta!

I suppose that could be a double-whammy then? If the temperature rises, the air can hold more water vapour in suspension before it precipitates out so that will start a vicious circle...

atmosphere gets warmer...more water vapour held in suspension...as this is a really bad greenhouse "gas", the atmosphere warms up some more...so it can hold more water vapour in suspension...and so on!

Soon we won't even need any CO2!

It does have a cat.

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

The nitrogen in the atmosphere is used as an expansion medium, which when heated by the burning exerts a force on the piston.

An internal combustion engine could run on pure oxygen, but do this to your existing car and it'll run extremely weak unless you pump in five times as much fuel at the same time.

Of course then you'd start melting pistons, bending conrods, breaking crankshafts and probably burning valves too with all the extra heat generated.........



Exhaust gas recirculation is a technique employed to reduce fuel consumption by reducing oxygen content in the charge.

All you want is a gas which will expand massively and quickly. You don't actually want it all to combust and vanish, otherwise you'll get no power.

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Blimey! So it is. PV=nRT

I never noticed that before. How much of the power output comes from expanding nitrogen? 10%? 5%?

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

Blimey - you got a bloke in the office like that too ??

I'd have thought the answer to that was "none". The nitrogen expands with the heat created when the petrol and oxygen burn but doesn't actually "provide" and energy into the system at all....

????? Does that make any sense?