Exhaust Gas Recirculation / Inert Gas Injection

[whipped]

In the interest of saving fuel....

From what I understand, an EGR system on an engine can't go above some certain % exhaust because of heat, impurities and reactive chemicals in the exhaust... (You get detonation)

Well if you want to turn your 3.0L V6 into a 2.5L I4, why not try injecting CO2 into the intake and cutting back on the fuel? Sort of like a N2O system in reverse. There are 20# cylinders for $150 (new) online, which is something around 200 cubic feet of CO2. I'm lazy to do the math, but at 2000rpm (typical cruise RPM), air flow is fairly low. Will it last an hour? I don't know. Will the gasoline savings offset the CO2 gas cost? I don't know. Obviously the ignition would have to advance to compensate for the slower flame front as well. Discuss....

[The Dark Side of Will]

I haven't run any numbers, but my gut feeling is that the CO2 would run out fairly quickly and wouldn't be economical.

The whole idea behind EGR is that it's not *supposed* to be be reactive. It's supposed to be inert material introduced into the intake tract to reduce pumping losses. The EPA likes it because it keeps peak combustion temperature down and NOx formation along with.

The detonation problem comes from the temperature of the exhaust gas. That's why diesels and engines that make extensive use of EGR have EGR coolers. The Northstar's water log doubles as an EGR cooler. That's one reason it's as bulky as it is.

I think there was an experimental diesel engine someplace that used extremely high volumes of EGR to achieve very high fuel economy.

Thinking about the "in cylinder EGR" that LS engines use (IE, a higher overlap cam leaving exhaust gas incompletely scavenged under light load conditions), and idea comes to me...

What if BMW's Valvetronic were used on the exhaust cam? It could still throttle the engine by not allowing enough exhaust gas out to make room for the intake charge... at low power it would be virtually free of pumping loss, yet only burning a small amount of mixture. The temperature is an obvious potential problem, so it may have to be built like a diesel... or just have more cooling system capacity.

[whipped]

It can't be that temperature is the only thing affecting the combustion, when finned aluminum blocks are so cheap. Why can't we have throttle-less gasoline engines that adjust EGR % to adjust torque? Eliminate pumping losses altogether?

Combustion must just not be stable at low O2... how can we fix that?

[The Dark Side of Will]

Solve that problem and you'll have the better mousetrap

[teamlseep13]

The whole idea behind EGR is that it's not *supposed* to be be reactive. It's supposed to be inert material introduced into the intake tract to reduce pumping losses. The EPA likes it because it keeps peak combustion temperature down and NOx formation along with.

The detonation problem comes from the temperature of the exhaust gas. That's why diesels and engines that make extensive use of EGR have EGR coolers. The Northstar's water log doubles as an EGR cooler. That's one reason it's as bulky as it is.
.

EGR is only meant to cool the combustion chamber because it reduces the amount of burnable mixture in the combustion chamber. Why cool the combustion chamber? It reduces the amount of oxides of nitrogen in the exhaust gas. Pumping losses aren't the reason EGR vavles were put into use.

Remember, diesels can't detonate, per say. They don't cool the EGR gases to prevent detonation. EGR gases are cooled before being routed into the intake manifold for the reason of dropping the exhaust gases to a temperature where carbon will not form on important sealing surfaces such as EGR pintles, intake valve seats and the like. Otherwise pintles would stick and the whole thing shits the bed.

The Northstars water pump housing didn't cool the gases enough because the early ones with the per cylinder EGR distribution ports got clogged with carbon at high miles and caused the weirdest running conditions. They got rid of that fast.

BMW's Valvetronic would be cool on the exhaust cam but like you said, I can see things getting hot really really quick.

[The Dark Side of Will]

EGR is only meant to cool the combustion chamber because it reduces the amount of burnable mixture in the combustion chamber. Why cool the combustion chamber? It reduces the amount of oxides of nitrogen in the exhaust gas. Pumping losses aren't the reason EGR vavles were put into use.

Remember, diesels can't detonate, per say. They don't cool the EGR gases to prevent detonation. EGR gases are cooled before being routed into the intake manifold for the reason of dropping the exhaust gases to a temperature where carbon will not form on important sealing surfaces such as EGR pintles, intake valve seats and the like. Otherwise pintles would stick and the whole thing shits the bed.

The Northstars water pump housing didn't cool the gases enough because the early ones with the per cylinder EGR distribution ports got clogged with carbon at high miles and caused the weirdest running conditions. They got rid of that fast.

BMW's Valvetronic would be cool on the exhaust cam but like you said, I can see things getting hot really really quick.

Yeah, my statement was poorly worded. The primary reason EGR is in place is to reduce peak combustion temperatue and keep NOx down. The reduction of pumping loss is a secondary effect.

My temporary engine for The Mule was a '93. I filled the EGR slots in the ports and used '95 manifolding. The Mule's current engine uses the later cylinder heads that do not have the EGR ports/slots with the '93 water log that does not have the external EGR port for the tube that goes to the throttle body spacer. Win/win.

[teamlseep13]

That is cool that you swapped heads, those EGR slots are nightmare-ish on high mileage engines.

[The Dark Side of Will]

I can imagine... not sure what engineers were thinking when they developed that. I guess they didn't realize that exhaust gases contain soot and carbon...
It's not like EGR tubes can get coked up on high mileage engines or anything...

The current FSi Audis have trouble with carbon deposits on the intake valves. EGR and PCV gases flow by the hot valves and some of the soot and oil stick. Since the engines are direct-injected, there's no constant spray of fuel on the valves to keep them clean and they develop some pretty impressive deposits.

[teamlseep13]

I can imagine... not sure what engineers were thinking when they developed that. I guess they didn't realize that exhaust gases contain soot and carbon...
It's not like EGR tubes can get coked up on high mileage engines or anything...

The current FSi Audis have trouble with carbon deposits on the intake valves. EGR and PCV gases flow by the hot valves and some of the soot and oil stick. Since the engines are direct-injected, there's no constant spray of fuel on the valves to keep them clean and they develop some pretty impressive deposits.

The 3.6L DI motors have this issue too. Done quite a few top engine cleans to cure valves hanging open because of carbon on them....