CAN DO CAMBUSTION
Remembering that all emissions regulations are dependent on accurate measurement of exhaust gas constituents, one of the leaders in providing first-class equipment for such measurement is Cambustion, a Cambridge, UK-based company. Chris Nickolas, senior engineer for Cambustion, takes up the story: “The company was started in 1987 by some guys from the engineering department within Cambridge University. They had been doing extensive research on engines as part of their PhDs. They come up with the idea of taking a standard emissions bench hydrocarbon analyzer, Which at the time had a fast response time of about a second. They realized that if you could make this a lot faster, then you could suddenly start seeing much greater detail.”
Thus was founded the fundamental raison d’etre of Cambustion, the development and manufacture of high-speed-responding gas analysis instruments. “If you get it fast enough, within one cycle you can start to see things like exhaust valve leakage, or the effects on a two-stroke and of valve overlap, so you can look at how much fuel is going up the exhaust,” explains Nickolas. “Since then, we’ve got fast NOx, fast CO and CO2 measuring instruments, and in the last five years, we’ve developed an instrument for looking at diesel particulates for aerosol measurement,”
Today, Cambustion instruments are in use all round the world, by all major engine and vehicle manufacturers. The company has an engineering services side as well, with chassis and engine dynamometers, and a lot of emission equipment, so that they can perform engine test work, meaning that “as instrument developers, we have an understanding of what it’s like to do engine tests, and we can also test our equipment”.
In a world that’s embracing environmentally-friendly technologies, the exhaust system of an internal combustion-powered vehicle is often only mentioned with an implied sneer. Yet until the engine is replaced by an electric motor, whether driven by batteries or fuel cells, the exhaust remains a vital part of the IC engine.
The research and engineering effort that has gone into cleaning exhaust gases in recent years has been highly impressive.
In Germany, Wescast engineers construct cast iron and cast steel exhaust manifolds, and have evolved a high-precision casting technique that provides wall thicknesses of under 3mm in Simo grade (a silicon-molybdenum alloyed ductile iron) or Niresist grade (D5S, a 35% nickel ductile cast iron). Klaus Kampendonk, director of sales and engineering for the supplier, says that such an achievement provides a manifold with less mass and less thermal inertia so that warm-up time and the catalyst light-off time from a cold start is reduced.
One of Wescast’s most recent technical innovations is an integrated manifold design, meaning an exhaust manifold cast system as one unit with a turbocharger casing. As well as improving structural strength, and placing the turbo closer to the exhaust ports-which is good for better throttle response-this eliminates the mounting flanges and the need for a sealing gasket.
The catalytic converter has long been regarded by many in the automotive industry as the key innovation to cleaner exhausts. It may have been invented three decades ago, but there has been some development of various aspects to the cat that we know today. One important factor is the design and production of the substrate or internal carrier of the catalytic materials within the converter casing. The delay following a cold start before the catalytic converter warms up for active use means that the engine is exhausting itself with uncleaned air, so the shorter the light-off time, the better. One obvious way to achieve this process is to combine reduction of the thermal mass of the substrate with, if possible, a choice of substrate material that is heat-conductive.
Various ceramic materials still have a strong grip on the auto catalytic converter sector, and suppliers like Corning in the USA specialize in the ongoing development and manufacture of such substrates. Corning’s Duratrap brand includes an aluminum titanate diesel particulate filter brought in during 2005 and introduced in September 2007, an advanced cordierite filter for light-duty diesels. Spurred on by the interest in diesel power in the US market, the largest interest amongst catalytic converter manufacturers is currently in reducing diesel pollution.
Finnish company Ecocat is heavily involved in metallic substrates, which the company manufacturers itself in-house along with the rest of the catalytic converter. The company’s CTO, Toni Kinnunen, explains: “We use a standard grade steel-an iron chrome alloy-not a pure stainless steel that is corrosion-resistant and can maintain its properties and is durable up to 1,100oC.” But when asked if he can supply figures for time to light-off, Kinnunen is cautious, pointing out that Ecocat’s ceramic substrate competitors have done considerable development to improve light-off time by going for thinner wells between cells. According to Ecocat’s CTO, a comparison done a little while back between ceramic and metallic substrates of similar mass and mesh size-400-500 cells per square inch-showed that while the ceramic catalytic converter achieved 250oC from cold in around 65 seconds, the metallic substrate managed the same temperature in about 25 seconds less. Kinnunen adds: “Fundamentally, the ceramics are insulators and metallics are conductors, so there must be a difference.”
Ecocat’s most recent hi-tech achievement is the particle oxidation catalyst (POC) for light-and heavy-duty diesel applications. This device combines the roles of a diesel oxidation catalyst and a particulate filter. It differs from earlier similar ideas by using a foil rather than a screen as substrate. A washcoat-applied layer of catalytic material regenerates the collected particulates by forming nitrogen oxide (NOx) and oxidizing hydrocarbon (HC) particles. This provides a device that compared to a traditional DPF does not block and cause excessive back-pressure, even if for some reason the regeneration is delayed, especially as exhaust gas can still pass through the POC along the substrate channels.
Another innovative system is the latest diesel catalyst from Argillon. It achieves standards of sufficient cleaning to meet US 2010 and EURO 6 emission regulations, with a homogeneous zeolite-based material that can be extruded, and also provides a 100% active honeycomb for NOx removal, unlike an inert substrate that has to be coated.