Best way to detect vehicle exhaust? - Page 1
Forum section: electronics / projects

author: Ampere
author_rank: Regular Contributor
timestamp: April 12, 2017, 06:12:12 pm
content: I'm working on a project which includes a safety system for detecting vehicle exhaust. I've run into a few problems:CO2 detectors add too much to the cost of the project. The ones I've seen start at $93.CO detectors would work for petroleum engines, but diesel engines don't produce much CO.Other concentrations seem to depend on the state of the engine, IE not present while idling.Am I missing something obvious here? Would a generic smoke detector module work in this situation? All I need is something that will tell me when there's too much exhaust in the area so that the micro can do the rest. Preferably something off-the-shelf because there's a possibility that more of these will be made.Edit: To clarify, this system will need to work with both petroleum and diesel engines.

author: Gyro
author_rank: Super Contributor
timestamp: April 12, 2017, 06:23:50 pm
content: I suspect that an ionisation type smoke detector would work reasonably well with diesel exhaust. Maybe a catalytic type hydrocarbon detector too.It sounds as if you may need a combination of detector technologies to provide reliable detection in all cases.Maybe you could add more detail of the environment - if it's a safety system I assume it's something like an enclosed garage space? Cold engines will of course be much easier to detect than engines that are already up to operating temperature, not sure if that is relevant to the situation. What about an acoustic sensor solution (maybe with a DSP)?

author: fcb
author_rank: Super Contributor
timestamp: April 12, 2017, 06:25:18 pm
content: What about a microphone?

author: CJay
author_rank: Super Contributor
timestamp: April 12, 2017, 07:21:17 pm
content: Electrochemical O2 sensor, mV output which drops when the level of O2 drops, you need to periodically 'zero' them with fresh air to deal with the output dropping as the cell wears.

author: thm_w
author_rank: Super Contributor
timestamp: April 12, 2017, 10:09:13 pm
content: CO2 sensor is fairly cheap, I use the MH-Z19 and it is very good ($28). MH-Z14 is also available but oddly more expensive.From the link below, output of exhaust is 6-8% (so 60-80,000 ppm). The MH-Z19 range is 0-5,000ppm which should be fine, if you go above that level it will just clip at 5,000. I don't think you will get any false triggering (400-2000 ppm CO2 are typical levels). Sounds like CO2 is the way to go.O2 sensor is not cheap (discussed in another thread), $50 and up, and has lifespan issues.QuoteCO looks like its not reliable, after 5mins of running these guys detected 0ppm of CO. That is quite surprising:http://www.gastec.co.jp/english/kids/experiment_download/car_exhaust.docParticulate sensor is an idea but surprisingly modern diesel is relatively clean and you may get false trips from other sources (cigarette smoking produces way more than a clean diesel in a closed garage).I can send you my report if you are interested, might be relevant for you. I will post it here in a few weeks.

author: ratio
author_rank: Regular Contributor
timestamp: April 12, 2017, 10:26:51 pm
content: We have been installing combo CO/NOx systems fromhttp://www.armstrongmonitoring.com/lately, to operate exhaust fans in automotive garages. I understand them to be significantly cheaper than thewww.honeywellanalytics.comwe had been using, but they're still not at all cheap.

author: MagicSmoker
author_rank: Super Contributor
timestamp: April 12, 2017, 10:29:24 pm
content: I have no experience with this company or website, but was looking into them a few months ago for a project that never went through:http://www.futurlec.com/Gas_Sensors.shtmlNote the CO sensor for $7...

author: LaserSteve
author_rank: Super Contributor
timestamp: April 12, 2017, 10:32:34 pm
content: Www.co2meter.comI've had good luck with their Usb products runningFor days and weeks in the lab with no issues.S.

author: thm_w
author_rank: Super Contributor
timestamp: April 12, 2017, 11:01:02 pm
content: Quote from: MagicSmoker on April 12, 2017, 10:29:24 pmThose are great to play around with and the only real option below $20.However, there are tons of cross-sensitivities to other gasses and the calibration would be very difficult.Also CO of 20ppm is already quite high (their spec is 20-2000 ppm), and there is no way you can reliably detect that with that sensor IMO.Its worth paying more for something you don't have to cal, and doesn't take half a watt.

author: james_s
author_rank: Super Contributor
timestamp: April 13, 2017, 12:00:09 am
content: I would be very careful skimping on sensors or taking any kind of shortcuts for something that is a safety system. Is this a personal project for your own use? With a product I worked on we had to be very careful not to market it as a safety device as that opened a whole can of worms regarding liability and whatnot.

author: Nusa
author_rank: Super Contributor
timestamp: April 13, 2017, 12:15:11 am
content: Sounds like whatever you do, you need a backup off-the-shelf CERTIFIED CO detectors to tell people to get out when your system has failed. Unless it's only your own personal life that's on the line, in which case you can do what you want. As for the less-lethal smelly stuff, people still have noses.

author: Ampere
author_rank: Regular Contributor
timestamp: April 13, 2017, 02:51:44 am
content: Thanks to everyone for the helpful responses! The device itself is NOT a safety device. It should never, ever be used on a vehicle in a garage, but... people are sometimes slow to think. I sold my team on the idea of including such a sensor as a courtesy to those who would do something so incredibly destructive despite all common sense. Rest assured that I will only use a proper CO2 sensor if we enter production. Even if it's not a safety device and even if it would be their own fault, I do not want anyone to be killed while using this thing.We're in the prototype stage right now so I think I will try to find a MH-Z19 module like the one which thm_w mentioned. Unfortunately, it looks like they only ship from China/Hong Kong so I may have to salvage a CO2 sensor from something for the first prototype. I can't wait a month while the sensor travels here on the slow boat.Quote from: thm_w on April 12, 2017, 10:09:13 pmThat answers my question perfectly, thanks. And I would definitely appreciate anymore information you have on this kind of problem.I'm a student so my experience in practical design is limited to very small personal projects I've done.

author: CJay
author_rank: Super Contributor
timestamp: April 13, 2017, 06:40:37 am
content: Quote from: thm_w on April 12, 2017, 10:09:13 pmThe MH-Z19 looks a far better option than the electrochemical O2 sensorand I'd recommend the OP to at least trial one but...O2 sensors are actually favourably comparable in price with the MH-Z19, a quick google of my old competitors shows I can still buy one off quantities at retail for $35 and I know the profit margins on those cells (I used to turn over ~200 a year and was buying them in for under $20 in boxes of 25) so $50 is a very high price for an electrochemical O2 sensor but as you point out, they do 'wear out' (roughly two year life or longer if it's not mistreated, *way* less if you abuse it) and can be poisoned if the sample has high concentrations of (IIRC) H2S from a cold, failing or faulty catalytic converter.I've been out of that game for a number of years now and hadn't realised how much the tech had moved on, the MH-Z19 is a *really* interesting bit of hardware and as others have suggested, looks way more suitable for the OP's needs, indeed, I've ordered one to play with for myself.

author: max_torque
author_rank: Super Contributor
timestamp: April 13, 2017, 12:04:43 pm
content: DO NOT use an O2 sensor to try to identify a hazardous atmosphere! (Unless you like being done for manslaughter).CO and CO2 kill people at low enough concentrations so as to leave the percentage of oxygen in the atmosphere plenty high enough to support normal life.Plenty of "Google info" is available on the subject.

author: CJay
author_rank: Super Contributor
timestamp: April 13, 2017, 04:13:30 pm
content: Quote from: max_torque on April 13, 2017, 12:04:43 pmMea culpa, you're right about CO and it'd be very difficult to reliably detect enough of a drop in O2 (thought there certainly would be one, I haven't done the maths, used to know this stuff off by heart, even down to the hideous formula for calculating Lamda from the hydrocarbon composition of the fuel) to alert the risk of danger.CO2 is not as dangerous as CO in low concentrations, 3% CO2 is considered maximum safe concentration so that *would* be detectable by a drop in O2 levels before it became dangerous.All of which is moot, the CO sensor the OP has been recommended looks more than adequate for the job (and when mine arrives I'll be comparing it to the government approved five gas exhaust emissions analyser that's sat in my shed, hopefully the bottle of calibration gas hasn't all leaked away.)

author: Siwastaja
author_rank: Super Contributor
timestamp: April 13, 2017, 04:57:24 pm
content: IMHO: you need at least two sensors: CO and CO2. If they are prohibitively expensive, then I'd just give up with the project. It makes little sense to do a vehicle exhaust detector which cannot reliably detect the exhaust. Both substances are dangerous, but on different levels, and they can be produced on different scales depending on the actual car, so you need to detect both separately.

author: james_s
author_rank: Super Contributor
timestamp: April 13, 2017, 05:04:47 pm
content: As far as I know, the only danger of CO2 is asphyxiation, it's not in itself toxic, but it's heavier than air and displaces oxygen. CO on the other hand is very toxic, the body treats it as oxygen but can't use it. Even relatively small amounts of CO in the air can accumulate in the body leading to confusion, disorientation and eventually loss of consciousness and death.

author: thm_w
author_rank: Super Contributor
timestamp: April 13, 2017, 09:24:04 pm
content: Quote from: james_s on April 13, 2017, 05:04:47 pmDepending on the level, CO2 will cause dizzyness, drowsiness, reduced hearing, reduced mental performance, and yes eventually death (~10% or something).CO for sure is more toxic but from that link I referenced, is not produced by the cars tested in any detectable level after 5mins of running.CO is one of those things where you'll almost never see it, but if you DO see it its a major concern.Quote from: Ampere on April 13, 2017, 02:51:44 amI will PM you a draft of my report + code.Look for a seller that offers ePacket ($4?), then it should arrive much faster. Anything more than that might be too much for you (ie fedex is $40).

author: den
author_rank: Contributor
timestamp: April 14, 2017, 01:08:42 pm
content: I would advise before doing anything on the project, do a research in google to get more familiar with the problem, because a lot of information given here concerning vehicle/engine stuff is false.CO2 concentration in exhaust of diesel and gasoline is different. Diesel is a quality-controlled engine, meaning CO2 concentration will increase with increasing load. Conventional gasoline, on the other hand, works with stoichiometric mixtures, meaning the CO2 concentration is approx. constant and is 12,0 - 14,5% depending on the calculation method (humid or dry exhaust) and fuel composition.Diesel doesn't emit any significant CO concentration (it's lean burn!), gasoline does have approx. 0.5% CO raw emission at normal operation. Raw, because there is practically nothing after the catalyst (if it works). All concentrations given are volume (molar) fractions.This is only relevant, if you plan to measure engine exhaust. If you are measuring these concentration in a room, then you should be interested not in concentrations of anything in exhaust, but in volumetric flow rate, because this fills you room, not the percentage. In this case, for example. CO2 vol. flow of gasoline and diesel are similar, although their concentrations in idle are quite different.

author: Nerull
author_rank: Frequent Contributor
timestamp: April 14, 2017, 05:46:15 pm
content: Quote from: james_s on April 13, 2017, 05:04:47 pmCO2 impairs respiration and inhibits red blood cells from taking up oxygen, so it will cause suffocation even an in environment with plenty of oxygen. It does not need to displace it. 10% CO2 in a pure oxygen environment will cause suffocation.The danger with CO2 being heavier than air is that this allows it 'flow' into low lying areas and build up dangerous concentrations, but it does not need to displace all the oxygen in the area to do so.It is non-toxic, much like pure oxygen is non-flammable. Technically true, but not the only danger.This is a very different mechanism than inert-gas asphyxiation, and shouldn't be thrown into the same group. Our blood cells need access to a low CO2 environment in order to exchange CO2 for O2.CO also inhibits uptake of O2, but at much lower concentrations, which makes it even more dangerous.

author: james_s
author_rank: Super Contributor
timestamp: April 14, 2017, 05:57:00 pm
content: That's interesting, I was not aware of that. Good to know.

author: Nerull
author_rank: Frequent Contributor
timestamp: April 14, 2017, 06:00:06 pm
content: Note that this was the big issue with scrubbers on Apollo 13 - they were not in danger of running out of oxygen, but if the CO2 levels got too high they wouldn't be able to breathe it anyway.

author: Gyro
author_rank: Super Contributor
timestamp: April 14, 2017, 06:46:30 pm
content: The only thing you have going for you with CO2 is that it has very noticable physical effects - it's the rise of CO2 that causes discomfort and a suffocating feeling.With reduced O2 levels, you go into hypoxia with no apparent discomfort, in fact there is a feeling of well being and dreaminess until it is too late to escape. I remember a documentary looking at less distressing alternatives of capital punishment (for the US), apparently breathing pure nitrogen is painless (and in fact gives the same euphoria feelings as above) as long as CO2 is purged, it was apparently vetoed for that reason (no suffering). It's possible for the human body to survive on less than normal atmospheric O2 levels though.The real killer is CO which will kill you without you knowing a thing about it. CO poisoning can become irreversible after a certain point, even if the patient is removed from the situation. It binds so well with Haemoglobin that it is difficult to replace it with Oxygen.I suspect that in a normal ventilated garage situation it would be difficult to deplete O2 levels sufficiently for it to becomethe primarydanger. I still think a combination of CO and fine particulate (ionisation) might still give a 'workable' level of protection, I uderstand the issue with false triggering due to people smoking - but it's probably best to detect this anyway because people shouldn't be smoking in garages - firstly because of flamable vapours and materials and secondly because they are 'pre-loading' themselves with CO.I know that catalytic converters reduce CO emissions by combining it with O2 - I wonder what happens to its efficiency in doing this when atmospheric O2 levels are reduced, likewise with the other pollutants.

author: den
author_rank: Contributor
timestamp: April 15, 2017, 07:59:51 am
content: Very good post.My only remark is on the particles - there will be a lot of particle sources in the garage, and there is actually not much coming from the engine, especially diesel with DPF, which exhaust contains even less particles, than normal air does.On CO oxidation - engine ECU assume 21% O2 in the air, so if this concentration is reduced, then the mixture (talking about gasoline of course) becomes reach, as a consequence CO will increase several times and the catalyst will not be able to oxidize it due to the lack of oxygen in exhaust. Catalyst works only with stoichiometric mixture (EDIT: this is assuming no lambda control. Lambda control will actually adjust the mixture back, but it also has its limitations)

author: PChi
author_rank: Frequent Contributor
timestamp: April 15, 2017, 08:04:06 am
content: What about measuring the exhaust temperatue? It's going to be easy to measure close to the outlet.

author: BrianHG
author_rank: Super Contributor
timestamp: April 15, 2017, 10:30:14 pm
content: Quote from: PChi on April 15, 2017, 08:04:06 amI was thinking the same, a FLIR camera should see plume of warm air. I also once seen a docu where they had a specially tuned narrow band far IR camera which pretty much only showed car exhaust exclusively. The placed the camera on a city street corner, and boy you saw all the exhaust, with a bit of residual from the vehicle frames, people and buildings.

author: fcb
author_rank: Super Contributor
timestamp: April 16, 2017, 09:15:01 am
content: Is your intention to create a device to warn of a car left idling (accidental?) Or to detect when there is a potentially hazardous atmosphere (let the owner idle the vehicle)?If the former, then a microphone feeding an FFT (which looks for a static frequency for longer than X second) would work, and be cheap. If the latter, then CO/CO2 detection seems obvious.