EXPLAINED: EGR TECH
ARE EGRS RUINING MODERN ENGINES? IT COULD COST YOU A $30,000 FINE TO FIND OUT.
IN A WORLD where free information reigns supreme, it’s often difficult to find the diamonds in the crap. All it takes is a quick search online to find thread after thread of ill-educated opinions sprouting off some nonsense about whatever happens to be the latest trend in internet-land. $30 canvas seat covers apparently as good as Aussie-made gear, humongous suspension lifts that’d rival Goliath in terms of size and likelihood of failure, and the latest hair-brained idea that seems to be gaining momentum faster than a rich, old billionaire – removing emissions equipment for such incredibly valuable reasons such as “it sounds better” and “me mate did it and loves it”. It’d almost be comical if it wasn’t having a serious effect on engine longevity.
What we’re referring to is the growing trend of tampering with and removing important emissions systems such as Exhaust Gas Recirculators (EGR) and Diesel Particulate Filters. To get to the bottom of it we’ve gone straight to the source, with three of the best diesel experts all throwing their weight into an on-going battle between good and evil, the underdog and the all-powerful government, and internet modifications and common sense. Enrolled this month are Andrew Leimroth from Berrima Diesel, Paul Farrell from Geelong Performance Centre, and Stephen Booth from PowerTorque Victoria.
MANUFACTURERS HAVE THEIR FEET HELD TO THE FIRE IN A BID TO REDUCE EMISSIONS
UNDERSTANDING EMISSIONS SYSTEMS
WE ARE big proponents of the internal combustion engine around here. They’re fantastic inventions that have given millions of people the ability to travel long distances with a load in relative comfort. That said, they do have a downside, and if we’re perfectly honest, it’s a real a doozy. Forget all the back and forth about climate change and emissions effects on the earth, it’s a scientific fact that diesel emissions cause lung damage, respiratory problems, acid rains, smog, and cancer in humans. It’s a direct result of the various emissions they produce such as Carbon Monoxide (CO), Hydrocarbons (HC), Nitric Oxide and Nitrogen Dioxide (NOX), and soot or Particulate Matter (PM). Scary stuff, right? It should be if you like breathing. The good news is manufacturers have their feet held to the fire by various agencies in a bid to reduce emissions and improve air quality. They’ve been forced to do this by implementing a few now reasonably common emission systems. “The two most types (of emission control) are Exhaust Gas Recirculation and catalytic convertors,” Andrew told us. “In more recent times Diesel Particulate Filters (DPF) have also become more common.” These three systems all work in varying ways. Catalytic convertors, most commonly found in petrol 4x4s and more recently in diesels, are used to convert carbon monoxide, hydrocarbons and nitrogen oxides into less harmful carbon dioxide, water and nitrogen. DPFS add another layer of complexity, aiming to break down large diesel particulates (soot) into smaller, less harmful ash.
Paul added: “Similar to a catalytic convertor, a DPF removes diesel particulates from the exhaust gas. There are pressure sensors either side of the DPF which are monitored by the vehicle’s ECU. When the pressure gets high enough, indicating a certain amount of blockage, the ECU commands what’s known as a burn. The injection timing is retarded, which heats the DPF to a very high temperature and burns the particulates out of the DPF.”
Another system known as SCR (selective catalytic reduction) injects a mixture of deionised water and urea, commonly known as Adblue, in a further attempt to reduce diesel soot. “It’s mostly in the American stuff,” Stephen added. “They’re usually a stage of emissions ahead of us.”
HOW AN EGR WORKS
WHILE most common emissions systems are designed to deal with harmful pollutants after they’ve been made – filtering them out in various ways – EGR is designed to prevent them being made in the first place. NOX is formed when nitrogen and oxygen molecules are present with temperatures north of 1500°C and is responsible for the smog often seen in cities, as well as acid rain.
As diesel engines rely on heat rather than spark to ignite, NOX has been a constant problem when talking diesel emissions. One way manufacturers have tried to curtail the production of NOX is to lower combustion temperatures. “What an EGR does is effectively plumb hot exhaust gas from the manifold back into the intake, re-burning exhaust gas.” Paul said. “The end result is less emissions out of the tail pipe.”
The net result of this is replacing flammable oxygen with inert exhaust gases, causing a colder combustion cycle and lower levels of NOX formation.
However, things aren’t always how they seem. Andrew brought up the point that while the basic design of an EGR system hasn’t changed drastically, their purpose has. “EGR was about NOX emissions before, but that’s sort of evolved with the new diesels having much lower compression than old,” he said. “Instead of running at around 450500psi they’re getting down as low as the 300s using high pressure common rail injection, precise timing and multiple injections to get a good burn at lower compressions.” All of this results in naturally lowered NOX emissions, leaving the EGR there for efficiency reasons rather than emissions.
“WE’VE SEEN INTAKE PORTS BLOCKED TO LESS THAN 50 PER CENT OF THEIR ORIGINAL SIZE”
THE BAD
ON PAPER an EGR sounds like a pretty damn good piece of kit to have on any 4x4, allowing the manufacturer to control combustion temperatures, reduce emissions, and do so with minimal complexity. Why then are so many people rushing to block off or even remove these systems? “Eventually the EGR gunks up the intake system,” Stephen said. “The combination of oil and vapor combined in the inlet manifold clogs it up.” The oil vapor he’s referring to is caused by engine blow-by, a completely separate operation in an engine, but one that causes catastrophic issues. Around each piston in an engine are a series of piston rings, designed to help seal the combustion chamber and allow the forces of igniting diesel or petrol to push down on the piston, rather than past it. The problem is these rings don’t make a perfect seal.
As the engine runs through its strokes small amounts of pressure are able to escape past the piston rings and into the lower half of the engine, pressuring the crank case. To relieve this pressure, manufacturers fit a breather to the top of the rocker cover that allows the oil-misted air to escape. Rather than this misted air venting into the atmosphere it’s plumbed into the intake, the result is a thin film of oil coating the inside of the intake manifold right through to the combustion chamber.
When the spent exhaust gases are reintroduced to the intake they stick to the oily residue and build up. “With the two of them combined it’s a recipe for disaster,” Andrew said.
“The inlet manifold gets blocked up, but it’s only because it’s all oily and wet. If the EGR was by itself it wouldn’t happen anymore than you would see in an exhaust pipe. It’s not really there to recirculate the soot, but by the nature of a diesel engine it does bring them through.”
Paul added that on his routine services he often comes across clogged intakes that require a full strip-down to clean. “We’ve seen the intake ports blocked down to less than 50 per cent of their original size.”