Has anyone ever used a combustion analyzer...

SlamDunk

on a vehicle? I bought a very used truck and while at work, thought I would check to see if analyzer would give me an idea if I would pass inspection. I selected nbr 2 fuel and came up with a CO of 5. Might be on the high side for a truck but it is probably not the best tool to use.

rick in Alaska

Always wanted to try it, but haven't. I wonder what would show up on the exhaust of most diesel trucks? Seems there are an awful lot of them running around that can be especially nasty smelling when you get behind them. Makes me wonder what kind of numbers I can see from the analyzer?
Rick

JStar

I've tried it on one of my work trucks. I have no idea what the numbers should be but my general assessment is that the readings were very lean and 50+ ppm of CO. That might be a result of an unsealed test area in the exhaust, though.

SlamDunk

I think placement in exhaust pipe will effect reading.

At idle, I read 30/40ppm. But after raising the rpm to around 1200, it dropped significantly. Not enough to pass emissions which is why I hope position in exhaust system matters.

ChrisJ

Make sure the truck is good and warmed up. Take it out on the highway for a few miles.

I always did this with older cars before going to inspection on a day where there was no line.

I thought the machines used at emissions facilities had some kind of test gas used to calibrate the machine every time or something?

captainco

As far as I know the current EPA standard for new car emissions on CO is 2000ppm. I don't think I have ever tested a vehicle that was under 200ppm. At a cold start up they are over 10,000ppm.
Not sure where those low numbers are coming from?

ChrisJ

captainco said:

As far as I know the current EPA standard for new car emissions on CO is 2000ppm. I don't think I have ever tested a vehicle that was under 200ppm. At a cold start up they are over 10,000ppm.
Not sure where those low numbers are coming from?

You're telling me that a ULEV or SULEV rated vehicle can produce up to 2000PPM CO?

I find that hard to swallow.

ChrisJ

Hatterasguy said:

ChrisJ said:

captainco said:

As far as I know the current EPA standard for new car emissions on CO is 2000ppm. I don't think I have ever tested a vehicle that was under 200ppm. At a cold start up they are over 10,000ppm.
Not sure where those low numbers are coming from?

You're telling me that a ULEV or SULEV rated vehicle can produce up to 2000PPM CO?

I find that hard to swallow.

A typical CO limit is 1%. A well tuned vehicle will get down below .2%.

HC limits are measured in ppm and are typically less than 100 ppm now. 10 years ago, you were doing well to stay below 250.

CO is not measured in ppm for vehicles.

Ah
That's why I'm confused.

SlamDunk

Hattarasguy beat me to it. I think the max in NC is 2% from reading online but the info is hard to come by. Here is the EPA link:
http://www.epa.gov/otaq/standards/light-duty/ld-cff.htm

They measure CO in grams/mile but down here we don't use dynamometers for inspection. Don't know how or what they measure. My analyzer read 5ppm. Useless number I guess

ChrisJ

Hatterasguy said:

SlamDunk said:

Hattarasguy beat me to it. I think the max in NC is 2% from reading online but the info is hard to come by. Here is the EPA link:
http://www.epa.gov/otaq/standards/light-duty/ld-cff.htm

They measure CO in grams/mile but down here we don't use dynamometers for inspection. Don't know how or what they measure. My analyzer read 5ppm. Useless number I guess

The EPA tests for the manufacturers do measure all gases in grams/mile. But, you need some sophisticated equipment and a chassis dyno for that.

The simplified equipment measures tailpipe emissions in %CO and ppm HC. It's impossible to convert to ppm CO without total volume.

The CO output on new vehicles is effectively nil. They are never allowed to get into an operating mode that generates excess fuel without sufficient air for combustion. It's a long way from carburetors.

Are you 100% sure of that?
Until the O2 sensor heats up the computer runs in open loop mode which is presets only. I'd bet those presets are biased rich to ensure no knocking or other problems. Modern O2 sensors are all heated so they get hot far faster, but it still takes some time.


Also, as far as I know all modern cars at WOT run a mixture of 12:1 or close to it and often produce visible smoke from unburnt fuel.

ChrisJ

Hatterasguy said:

Well, they soak for 12 hours at 70°F so, even with a cold start they get to open loop pretty fast.


The test includes all of the combustion products in open loop so they have to be quite careful in that region as well. They cannot run rich in that mode or they fail the test.


"Knocking" isn't ever going to occur until the cylinder temperatures rise. Most of them use a "knock sensor" to prevent it anyway so they can stay right near the edge.

With the higher HP generally available from most vehicles, they can effectively ignore the WOT condition because they never have to use it on the test. In that situation, they can calibrate WOT as rich as they want. If it is a low powered vehicle, there is one "hill" where they might need maximum power. If so, they'd need to be careful and couldn't use 12:1. This is rare today, however.

Been a long time since I did that work. I calibrated the '81 225 L6 in the truck with its very first computer (only for spark). Raised the highway fuel economy by a whopping 3 mpg from 18 to 21 mpg (with a three speed automatic). It was so impressive that they had to spring for the $60 box.

Here we are 35 years later with a truck that has full computer controlled fuel injection and an 8 speed automatic and it still only gets 18 in the city and 25 mpg on the highway.

Not sure what you mean regarding something soaking? Also I assume you mean reaches closed loop fast?

Regarding knocking when cold, a gasoline engine most certainly can knock when cold, in fact I had one that knocked horribly when cold due to a bad vacuum sensor (didn't figure that out until the car was long gone). Also, part of the problem was the computer ignores knock sensors until in closed loop, so once again, you need to keep it slightly rich.

Not sure what you mean by maximum power, any car that I've seen at WOT runs 12:1 or close to it, and that is included in their emissions tests at the factory I would assume. This is one big thing a so called "tune" changes. They lean the mixture out at WOT to produce more power but at a greater risk. Obviously the risk of knocking is greatest at WOT.


Actually, according to these maps they go even richer than 12:1 now days.

captainco

.01% = 100ppm
.1% = 1000ppm
.2% = 2000ppm current EPA auto levels
1% = 10,000ppm
2% = 20,000ppm