Increasing EGR flow for better mileage

[Daox]

I've been mulling this around for a while now and its definitely an area to look into. How can we use EGR to increase our FE?

EGR could allows us to decrease pumping losses for the same power output, somewhat similar to lean burn. However, it doesn't have the NOx problem that lean burn does since there is not an overabundance of oxygen in the air/fuel mixture.

Lets take a look at how the OEMs utilize EGR. From this Toyota article, it seems they are using it solely as a means to decrease NOx emissions. I think this can be backed up by noting that the 96 Paseo had EGR vs the 97 which did not, and the 97 has a higher EPA mpg rating. So, we need to figure out how to alter EGR for our uses.

Quoting the article:

High EGR Flow is necessary during cruising and mid range acceleration, when combustion temperatures are typically very high.
Low EGR flow is needed during low speed and light load conditions.
No EGR flow should occur during conditions when EGR operation could adversely affect engine operating efficiency or vehicle driveability (engine warm up, idle, wide open throttle, etc.)

Why would we not want high EGR flow at idle and light loads? Pumping losses are the greatest when the throttle is closed or close to it. Low speed city driving mileage would be noticeably improved.

I also think real gains could be had if EGR flow is increased at cruising loads to further decrease pumping losses. This will have a downside, loss of power, but I think many here are willing to give some up. Also, if we again make it similar to learn burn, we could simply make some override switch that pops us out of 'EGR mode' and back to normal mode for power.


Now, I don't think any of this would be real easy to implement, but I really think its worth considering. There are definitely problems with EGR. First off it is hot, and its also messy (carbon build up). There are additional things such as ignition timing that would need to get looked at to make it a perfect system since an EGR rich mixture will burn slower and require additional ignition advance. There is also a point at which you can no longer dilute the intake charge without causing misfires (same as lean burn), so you can only take EGR so far.

I'm really looking for input, and ideas on how we could use this, the different systems out there, and how control them. I really only know Toyota. Their setup is described in the PDF I linked to. I also know Honda's Insight uses EGR, but it has an electronic actuator that opens and closes the valve. What do other mfgs use?

[TestDrive]

Some people/cars claim a FE gain with cold air intake.

I wonder if those cars EGR valves (assuming all have EGR) share some common method of control?

[SVOboy]

I think the main issue here will be computer regulation. Perhaps it would be better to change the valve timing to burn a bit more of the exhaust instead?

[Shawn D.]

Originally Posted by Daox

Why would we not want high EGR flow at idle and light loads? Pumping losses are the greatest when the throttle is closed or close to it. Low speed city driving mileage would be noticeably improved.

As the quote you used yourself said: "No EGR flow should occur during conditions when EGR operation could adversely affect engine operating efficiency or vehicle driveability (engine warm up, idle, wide open throttle, etc.)"

At low throttle openings and low engine speed, EGR makes the vehicle run extremely roughly -- I've experienced this myself.

[Daox]

Haha, that would make sense wouldn't it? I suppose the EGR rich mixture would cause the misfiring at idle pretty quickly.

[PaleMelanesian]

EGR actually LOWERS cylinder temperatures. Sure, it's hot, but in the combustion cycle there's less air/fuel that actually burns and produces heat.

[getnpsi]

A coworker's EGR is stuck open. It runs like an animal until its halfway warmed up. Without huge amount of ecu interfering driveability suffers because it's confused.

The math whizzes should chime in but I read somewhere that a functioning EGR effectively takes away a good 20% of combustion volume, so a dumb guess would to pull at least that amount of fuel as an experiment. I wouldnt try this in the city, but on a level stretch of road where id have a chance to monitor vacuum and other gizmos id be interested. There are plenty of thermoswitches and actuators on old 1970s and 1980's cars that can be implemented.

[MetroMPG]

You've probably seen our friend Julian Edgar at Autospeed has tweaked his car's (1st generation Insight) EGR with some positive results on fuel economy:

Tweaking the EGR, Part 1

I think it's absolutely worth investigating - since I've switched primarily to driving with load on the open road, I'd love to be able to optionally go into "EGR mode".

As has been mentioned, driveability can be an issue with too much EGR (regardless of load). However I suspect some ecomodders would be willing to sacrifice some amount of power, smoothness, & throttle response under cruising conditions if we can control the extent of it and when it's active.

I know I would.

[MetroMPG]

PS: anyone planning to mess with EGR will need an MPGuino or equivalent to properly measure the effects on fuel consumption.

The ScanGauge will not report fuel consumption properly under high EGR concentrations for the same reason it doesn't work well with lean burn.

[MetroMPG]

PPS - anybody know where the EGR valve is on the Metro?

I had a quick look the other day and couldn't find it. I know the Suzuki 1.0L's have it - because a coked up middle EGR passage in the head is a common problem in older cars that can apparently lead to a burnt exhaust valve in the #2 cyl.