Hot Heads: How and Why Audi Cools its Exhaust Manifolds

Hot Heads: How and Why Audi Cools its Exhaust Manifolds

Hot Heads: How and Why Audi Cools its Exhaust Manifolds

0 comments 📅21 June 2018, 17:45

The new 2.0-liter TFSI engines that blow in in the A3 and TT have some pretty neat features to boost power and improve experience. There are electric wastegates, a lighter cylinder block, plastic oil pans, thinner cylinder walls, aluminum fasteners, and more. But the coolest on the third-crop of the engine is the integrated exhaust manifold with liquid cooling.

Why on earth would an automaker crave to cool the exhaust? Especially on a turbocharged engine? This is how (and why) it works.

It starts with an clear out manifold that’s integrated into the cylinder head. Instead of the four detach exhaust ports you’d expect to find on a four-cylinder engine, there are justified two holes in the center of the head. That’s because the exhaust passages chance on up inside the head instead of outside, in a separate manifold.

Ditching the old-fashioned drain manifold is good for a few reasons. The turbo is bolted directly to the head, putting it not quite on top of the exhaust valves, helping the turbo spool faster. That means happier throttle response and the hotter exhaust gasses can lead to improved power harvest. On the other side of the equation, the catalytic converter can be mounted extra close to the machine, which reduces cold start emissions. That’s an alluring confederation and it’s why VW has been using an integrated exhaust manifold since 2013.

But that auxiliary hot exhaust can be bad for the cat once the engine’s up to temperature. The heat can cook the insides of catalytic converter and about it to fail, which is less good for emissions.

So Audi (and everybody else) needs a block out that keeps the cat and the turbo close to the exhaust valve, but that doesn’t cook with stiff exhaust temps. Oh, and it needs to warm up even faster, because getting locomotive and cat up to temp are the most important parts of emissions testing.

So the engine needs to be hotter and cooler, depending on how crave it has been running. Sure, no problem.

Enter the cooled integrated exhaust diversified.

Adding cooling to the exhaust manifold has some interesting effects. When you start the locomotive, the coolant starts sucking up heat directly from the exhaust. That warms the motor up faster. When the engine gets up to temperature more quickly, you get the engine to run in its most operative modes more quickly. One of the happy side effects of the setup for people of the north is that the car starts pumping impetuosity into the cabin more quickly.

Once the engine is warm, the coolant bath works to self-controlled the exhaust. With a turbo and a close-coupled catalytic converter, too much prostrate heat is an issue. That’s why some ’80s supercars had that uproarious Slow Down warning light. It was telling you the cats were overheating.

Unvarying engines reduce exhaust temperature by adding more fuel. Rich stimulus mixtures burn cooler but, as you might expect, that hurts your nuclear fuel economy. With the coolant bringing down exhaust gas temperature, the engine can run leaner. That saves stimulus when you’re cruising, and the cool temperatures prolong the life of the cat, the turbo, and your oil.

Pre-eminent of all, it doesn’t take much special plumbing. It’s just conformist coolant, run through the radiator like normal coolant would be. But by circulating it here the exhaust manifold, Volkswagen has made a vehicle that is cleaner, more likeable, and thriftier at the pump. And you don’t have to worry about rusted out exhaust manifolds 10 years down the avenue.

So that’s how Audi’s coolest exhaust tech works, and why they use it. Decent another way automakers are pushing internal combustion engine tech to levels that they no greater than dreamed about a few decades ago.

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