Since RDE systems require tailpipe-out (instead of engine-out) emission measurements, an extension has to be attached to the tailpipe(s) of the vehicle in which the emissions sensors are mounted. This extension usually consists of a one to two meter long tube that runs parallel to the back of the vehicle (back and forth for the case of the two meter length) and is attached to the vehicle’s tailpipe with a clamp. Due to the length and weight of the tubing, a structure is required to support the extension. The sensors are mounted as close to the vehicle’s tailpipe (ie. the clamp) as possible. The one to two meter length is long enough to ensure that the exhaust at the sensors is not diluted by ambient air that leaks in from the exit. The issue of dilution is more prevalent at low exhaust flowrates and for engines with low cylinder counts (ex. 1, 2). Although these one to two meter long extensions can be easily built, they take time to build, they take time to mount on a vehicle, and for some vehicles (ex. motorcycles) they are impractical.
A simpler sampling system can be made out a 300 mm piece of exhaust tubing attached to the vehicle’s tailpipe using a 100 mm piece of silicon hose and two hose clamps. The tubing is short and light enough that it does not need an external support structure. Similar to the one to two meter long system, the emissions sensors are mounted as close to the vehicle’s tailpipe as possible. With the short tubing length there will be dilution of the exhaust measured by the sensors, but it will only be at low flowrates. Fortunately, when vehicles go out of compliance, they go way out of compliance and therefore some dilution of the exhaust will not hinder the identification of “bad” vehicles. The advantages of these “shorty” sample systems are many: they are very simple to make, they don’t take long to make, they are inexpensive, they don’t take long to install, and they don’t require an external support system.
ECM has put together a kit of tubing, silicon hoses, and hose clamps that can be used to make shorty sample systems that fit most cars and light-duty trucks. All that is required before use is the welding of the sensor bosses to the tubing (as close as possible to the vehicle’s tailpipe as possible). ECM will even weld the bosses to the tubing if you send the tubing back to us marked where you want the bosses to be welded on.