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Dirty Stuff - Part 1

Getting the low-down on emissions testing - it's lot's more fun than you'd first think!

by Julian Edgar

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While lots of people who are into modifying cars start off at least a little interested in emissions, that interest usually wanes pretty fast when they realise how hard it all is. I mean, there're all these funny names - see-oh-two, nox, oh-two, aitch-see, see-oh (not to be confused with see-oh-two) - and these obscure things are all produced as a result of incomprehensible chemical processes occurring deep inside the bowels of the engine. And even if you do try to go the next step and get some kind of handle on what these weird names refer to, you're still stuffed because you can't measure them.

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Oh, sure, you can stick a gas analyser probe up the tailpipe and get some figures. But what do those figures signify? Do the percentages of different gases shown by the analyser have any relationship to emissions test cycles? If a car has a low CO (sorry, see-oh) reading at idle, does that mean it will past the test? Which test, anyway? It's at about this point that anyone who's sane throws their hands up in the air and cries 'enough!'.

In this short series we'll cover some of the basics of emissions. It won't be a chemistry lesson, and it won't be a full-on coverage of all the different aspects of emission control and measurement technology. But it will make the whole subject a whole lot clearer.

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The reason that we feel bold enough to launch into this is because for the first time, we can now show you the results of emission testing different cars. Bell's Auto Service, in Adelaide, has imported from the US an Air Kare 1000 emissions test system, which works with a specific Sun eddy-current emissions dyno. And proprietor Stephen Bell is as interested as we are in seeing the emissions performance of different vehicles.

Not only that, but he's also happy for us to make changes to fuel and spark and the cat converter and then see what these alterations do in an I/M 240 emissions test. The I/M 240 is the test used in most US states for ensuring that cars continue to meet standards - in Colorado, for example, cars must undergo an I/M 240 test every two years. Similar approaches are sure to come to Australia....

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How the I/M 240 test matches the Australian standard is a complex story. In short, the I/M 240 is based on the US FTP-75 standard (which was also adopted as the ADR37 Australian standard), but the I/M 240 test is a shorter version - 240 seconds instead of the FTP-75's 1874 seconds. The important point is that the I/M 240 test carried out by Bell's Auto Service's equipment is used to assess long-term emissions compliance in the US, and so the equipment is highly accurate and consistent. In short, it's perfect for putting different cars through their paces, and for modifying the tune of cars to see what then happens to their emissions cycle performance.

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Compared to a full emissions certification procedure (like that performed on a new car) the I/M 240 test is short and relatively simple - there's no SHED procedure to measure emissions from the fuel system (and plastics!) of the car; a certified fuel is not used; the speed of the fan at the front of the car is not specified; and a cold start does not occur. So whether or not an (Australian State) government would accept an I/M 240 test on (say) a modified car is still uncertain - and that will almost certainly be decided on a state-by-state basis anyway. It's sure a helluva lot better than the idle test that some authorities specify, though...

The I/M 240 Test

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The equipment uses a low power dyno (37kW maximum absorption) which has a great deal of inbuilt inertia (908kg). A low power dyno is all that is required because the power that the engine needs to develop never exceeds about 30kW (it varies, depending on the car), while the dyno's in-built inertia allows the accurate replication of coast-down, such as you get when you lift the throttle while travelling down a hill. In addition, a very accurate five-gas analyser is used, and - most importantly - a PC and its associated emissions test cycle software control the whole process.

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So what actually happens? In brief, the car is driven onto the dyno. The gas probe is exposed to air and zero'd. (Calibration of the system has to occur frequently and this is done using an expensive test gas.) The probe is inserted in the exhaust, and the driver is required to place the car in gear and then watch the PC screen. On the screen a narrow 'road' unfolds. The speed of the test car is represented by the location of a small car-shaped symbol on the screen - it's the driver's job to make sure that the on-screen car always remains on the road. The road angles upwards when the car is required to accelerate, alters to being horizontal when the speed needs to remain steady, and dives downwards when the speed of the car must do the same. On the screen the car is coloured green if it's on the road; if the driver wanders off, it turns red. Too many "high speed excursions" will see the test classed as invalid - only a small number of excursions are allowed.

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While the car is being driven through its test cycle, the nondispersive infrared (NDIR) gas analyser is being fed a constant sample of the exhaust gas. However, unlike a conventional workshop gas analyser, it doesn't calculate the results as percentages - the C0 as 0.7 per cent, for example. Instead, together with the speed being read from the dyno, it works out the emissions in grams per mile. In other words, the emissions test equipment outputs a mass per distance travelled - and that's very different sort of information from just percentages.

So that the dyno can place the right load on the car, the car's mass, mass on the drive wheels and Track Road Load Horsepower (a figure that takes into account rolling resistance and aerodynamic drag) needs to be inputted. The latter is calculated from a table that lists different car types (sedan, station wagon, etc) and the mass of the car.

The Test Cycle

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The shape of the speed/time curve of the I/M 240 test is shown here. In short, it is a 4-minute test representing a distance travelled of 3.1km, an average speed of 47.3 km/h, and a maximum speed of 91.3 km/h. The initial sequence requires a spurt of acceleration, as the car moves from zero to just over 40 km/h in about 14 seconds. Transients from about 24 - 32 km/h follow, before there's a period of 55-km/h cruise. The car's speed is then brought back to zero, before the second phase of the test begins. Through some more transients the speed is taken to 91.3 km/h with the car is cruised at this sort of speed for a while, before being brought back to zero fairly quickly (ie enough deceleration to require braking). Full throttle is never used, nor does the speed exceed 91.3 km/h (56.7 mph).

Incidentally, while all this detail may appear pretty academic, when you're actually doing some testing, the suddenness of the required acceleration, the long decel at the end of the test - and other seemingly minor points - can make for awfully big spikes in the gas curves. I'm getting ahead of myself, but just imagine if the acceleration enrichment of the engine management system is a bit high - then look at those three points in the test where hydrocarbons (HC) will skyrocket....

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As indicated earlier, this test is based on a portion of the FTP-75 test. That much longer test is shown here - even with the change in scale, it's still possible to see that the I/M 240 test pinches the bit that's used at the beginning of the Cold and Hot phases of the full test. Incidentally, you may be wondering where all these curves came from in the first place. Apparently, the 1975 FTP-75 shown here is based on a 1972 standard, which in turn was based on the data-logging of a chase car that followed a typical California commuter driving through Los Angeles rush hour on US Highway 4 in 1965! So, 35 years later, cars in expensive labs full of gas analysis equipment are being driven just like that commuter... weird, huh?

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Next week - we emissions test one of the cleanest cars sold in Australia - the Low Emissions Vehicle (LEV) V6 Honda Odyssey. And then we disconnect the two oxygen sensors, pull off the plugs to the coolant temp input and throttle position sensor and canister purge valve... and do the emissions test again! The results are quite fascinating.


Bell's Auto Service

08 8231 6211

0411 840 167

Bell Auto is happy to do one-off emissions tests for a quite low charge.

Dirty Stuff - Part 2
Dirty Stuff - Part 3
Dirty Stuff - Part 4
Dirty Stuff - Part 5

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