Is my car more sustainable with or without an EGR?

Question

I drive a 2003 Volkswagen Jetta with a 1.9 liter turbo-diesel engine. I often get well over 50mpg on the high way, and I love the fact that I have such a fuel-efficient car that is also fun to drive.

A few months ago, my check-engine light came on, and my local mechanic told me the EGR was bad. He suggested I could remove it (which I did). I did a bit of research on the issue, primarily concerned with the environmental impact of removing the EGR. I came to the conclusion that I wasn't really sure, but that the environmental pros and cons were nearly a wash.

Of course, the EGR is mandated by U.S. emissions standards, with the purpose of reducing NOx emissions. Although I have read claims that this is likely a misguided effort. Also, the addition of an EGR also increases other emissions. If my rusty memory serves, removing the EGR allows for more complete combustion, resulting in lower particulate emissions... And less restrictive airflow also improves engine performance slightly (by up to 2HP at high RPM for this engine, if memory serves).

And lastly, the removal of the EGR means I never have to clean the soot out of my intake manifolds again, which means fewer chemical cleaners, and less maintenance cost over the lifetime of my vehicle. And no EGR means the EGR can't break and need to be replaced again.

So all things considered, and legalities aside, is an EGR (specifically in a 2003 VW TDI engine) an environmental gain or loss?

Answer 1

Looking through some of your sources and thinking about the problem, it sounds like there isn't necessarily a definite answer, but a set of tradeoffs. NOx is associated with smog and acidification, particulates are related to respiratory health, and fuel efficiency is related to global warming (among other things like cost).

This problem would seem to be whether we value lower NOx emissions more than lower particulates and GHG emissions. If you don't live in a city, the answer might be that the NOx is less important because smog is less of an issue. If you do live in or commute to a city, it's more of a tradeoff, though with at least a 50% reduction in NOx, the 3% lower fuel economy and higher particulates (trapped by a filter which has production impacts, but we'll neglect those for the moment) probably make the EGR a better choice.

We could probably put some economic values on these various problems (particularly the non-climate-change ones), but the order of magnitude difference would suggest that the EGR is a good idea. In terms of climate change and fossil fuels, it's hard to argue that personal vehicles are ever sustainable, but your Jetta is a ways ahead of many other vehicles out there while we're still using cars.

Answer 2

You are moving the pollution from one area to another. Neither of which is sustainable. One just creates more solid pollution at end of life of the vehicle, the other creates more air pollution.

As you noted the EGR makes that your engine runs less efficiently under throttle. That results in wasted fuel and reduced power. Meaning you have to consume more fuel to get the power you need. The lab tests on this show favorable numbers for the EGR valve but in actual use someone driving in town accelerating fast from a stop can actually emit more pollutants. Under preferred (read low power) acceleration from stop you get great improvement in either case but the EGR vehicle will emit less CO, N₂O, CO₂ under the same amount of throttle, with a barely noticeable reduction in power.

Modern engines including your 2003 Jetta are computer controlled and require an active EGR to operate. Removing the EGR would require some serious hacking, and performance tuning. The systems are designed to run optimally with all components operating. If the EGR is not reporting expected pressures the computer is likely to cause the engine to perform less efficiently.

Regardless, there is nothing sustainable about the Jetta. It runs on a diesel powered Internal combustion engine, requires regular oil changes, and at end of life is a giant pile of fiberglass, plastic, and cheap metal that is not terribly recyclable. There is quite a bit of aluminum alloy in the frame. This is less recyclable than steel and often cost prohibitive to re-purpose. In terms of sustainability the EGR valve is practically irrelevant.