How to Eco-drive the VW PD TDI Diesel

[cRiPpLe_rOoStEr]

Originally Posted by mwebb

watch out for thermal shock

This is not a major issue at all. A properly-dimensioned water injection is just like some sort of "chemical intercooler".

on the theory that there will be no liquid h2o in the exhaust stream , it will all be in vapor state due to the heat / temperature in the exhaust

It vaporizes while it absorbs latent heat from the intake air. When some alcohol is added to the water, usually methanol but it could also be ethanol (even the good old Everclear may serve as it's quite similar to the E96h used as a motor fuel in my country), it vaporizes quicker.

you do not want to crack the substrate in the DPF or the thimbles in the lambda sensors

Water injection won't lead to a risk of cracking the DPF core or the lambda sensors. Otherwise, it would already be an issue to drive on a rainy day, which does a roughly similar effect to water injection.

EGR is good
more EGR is better than less to a point and defeating a properly function ing EGR does not improve fuel economy or power as
EGR does not operate at high load anyway .

EGR may have some benefits under certain conditions, but it doesn't prevent water injection to fare better on other conditions. By the way, while EGR has been pointed out to increase particulate matter emissions, water injection can decrease both NOx and particulate matter simultaneously.

[COcyclist]

Originally Posted by mwebb

EGR is good
more EGR is better than less to a point and defeating a properly function ing EGR does not improve fuel economy or power as
EGR does not operate at high load anyway .

carbon buildup is mostly caused by the driver and bad gas

This has not been my experience and is counter to everything I have read about making Diesel engines run better (although perhaps with higher emissions).

This thread is about driving for mpg which means long periods of low load. This is the type of condition that caused carbon buildup for me in the past. After the tune, which defeats EGR after warmup, my Italian tuneups to blow out carbon are needed much less frequently and show much less carbon when I do.

Also, remember Dieselgate? The cars that VW allowed to cheat the US EPA test performed worse in power and mpg after the VW fix. They cleaned up emissions by calling for more high pressure and low pressure EGR. We had an A3 TDI “Clean Diesel” in the fleet. Even in the factory cheat tune it never came close to the mpg I could get out of the PD TDI.

There is one instance where EGR may help mpg and that is during cold starts. My friend has an 02 TDI and did an EGR delete. This removed the EGR cooler so the exhaust gas no longer warms the coolant on startup. It takes time and a few hard pulls before he gets much cabin heat. FWIW I did not remove the EGR cooler in my TDI for that reason.

[mwebb]

" .... This is not a major issue at all. A properly-dimensioned water injection is just like some sort of "chemical intercooler". ..... "

maybe
how ever
an IMproperly designed water injection system can be an engine killer

( many / most of the discussions regarding water injection on these very pages in this very forum would be
IMproperly designed for varying reasons. imho
and would ultimately result in catastrophic failure )

and
a lambda sensor killer
and
a DPF killer

so i would say it can be a very major issue NOT to be attempted by someone UNwilling to add those UNimprovments to his or her car , during the course of the experiment

we all pick our own paths , and , we are liable for our own actions when we pick the wrong path

[mwebb]

....
This thread is about driving for mpg which means long periods of low load. This is the type of condition that caused carbon buildup for me in the past. After the tune, which defeats EGR after warmup, my Italian tuneups to blow out carbon are needed much less frequently and show much less carbon when I do. .....

right
EGR does improve fuel economy by displacing combustion chamber volume with an INert gas (exhaust gas with no or very little 02) that does not support combustion
so EGR makes the engine smaller at cruise AND reduces NOX by reducing combustion pressure wich in turn reduces combustion temperature so it is not as easy for N to combine with 02 to form NOX as that takes place mostly above 2500f .

less combustion chamber volume = less fuel consumed as fuel rate is determined by MAF flow on the mk4 system (primarily) . and MAF can not measure EGR flow so only counts the fresh air charge coming in .

poor quality fuel does not completely combust so it leaves carbon deposits
which decrease flow in the intake add turbulence to flow and INcrease compression ratio & screw up the swirl in the combustion chamber
none
of
those
things
are an improvement in Fuel Economy

EGR is good
carbon deposits from FREDs fuel is bad

[MeteorGray]

A good water injection system will keep combustion chambers clean of carbon. Such systems are useful for keeping exhaust gas temperatures at safe levels under heavy loads.

[Piotrsko]

Depending on where you water inject. In mine I fear water since it tends to park in the intercooler, make indegestible mayonnaise, and bend #3 rod.

[COcyclist]

We are entering summer here in the northern hemisphere. This may be a good time to talk about limited use of A/C for increased mpg. In short, the energy to run the compressor and fans comes from the engine. If you run the A/C a lot your mpg will suffer. What can you do so you don’t suffer from heat in the cabin? In no particular order...

1. Park in a garage or carport if possible so your car is not roasting when you enter it to start your trip.

2. Tint as much of the windows as is legal in your area.

3. If you must park in the sun, use a high quality sunshade in the windshield. A couple of US accessory manufacturers make some that are custom fit to the specific car. You could go a step further and make side and rear insulating shades. I did this on my little camper van and it makes a huge difference. There are plenty of how-to videos on YouTube.

4. When you return to a hot car, use the key in the driver door to hold “unlock” for 5 seconds to roll down all the electric windows at once, to let built up heat out before you drive (if it is hotter inside than out). In town at slow speeds where aerodynamic drag is lower, drive with the windows down for maximum ventilation.

5. On the highway there is a huge drag penalty to driving with the windows down. Roll up windows and use the fresh air vents directed on the parts of your body you want to cool. If you are driving solo, close off or redirect vents on the passenger side. If it is really warm I will open a passenger side window slightly to increase flow through the cabin.

6. Dress in the lightest clothing you can. On the hottest days I wear shorts and flip flops with a thin synthetic wicking shirt in light colors.

7. Prepare “cooling towels” pre-soaked in a small cooler so you can change them out as they warm up and dry out. I drape these around my neck and shoulders to extend my comfort range. I have also experimented with a chiller designed to reduce swelling after an injury. It circulates ice water through a pad that I place between my shoulder blades. I run it on a small inverter plugged into a lighter socket. It works great but requires more preparation than the cooling towels.

If you have passengers it may be better to run the A/C on “recirc” so you are not pulling in hot outside air. I rationalize that my per passenger mpg goes to 100 mpg, using only slightly more fuel to transport twice the cargo. My spouse is unwilling to do the silly hypermiling tricks when it comes to comfort.

8. If you must do extended engine braking on long hills, by all means run the A/C on high to help slow the car. Diesels do not engine brake like gas cars so I take advantage of some extra chilling at no mpg penalty while in DFCO.

[cRiPpLe_rOoStEr]

Originally Posted by Piotrsko

Depending on where you water inject. In mine I fear water since it tends to park in the intercooler, make indegestible mayonnaise, and bend #3 rod.

That's why an intercooler bypass for cold-starting and fitting the water injection nozzle after the intercooler are good measures to ensure safety.

[COcyclist]

I had the “opportunity” to be a courier for some medical supplies last week on some of Colorado’s great two lane paved mountain roads in the Golf TDI. I was reminded of a couple more tips for mpg. FWIW I averaged 50 mpg with spirited driving and some use of A/C and even a short construction zone on the interstate segment.

We have discussed DFCO and engine braking in previous posts and I was doing a lot of that. I also was trying to conserve momentum through the corners so I would have less acceleration losses coming out of the corners. I am running stock tires. One of the 4 is the original spare from the trunk. When the original Goodyears wore out I only bought 3 and mounted the spare from the trunk on one of my alloy rims. I changed the original shocks to Koni Reds with the front struts one click out from full soft. It firmed up the ride a little but really helped in the handling department. A very worthwhile upgrade in my opinion. Carry momentum as much as you can do safely.

While we are on the subject, weight reduction helps in handling, braking and acceleration, and generally improves mpg. I have removed the rear seat and replaced it with a lightweight flake board flat shelf. I carry my bicycle or skis inside instead of outside on a rack. I took out the spare tire and kept the jack and a can of tire inflator, which I have still never needed. I replaced the muffler with a straight pipe (don’t worry, the catalytic is intact). Total weight removed is about 100 lbs. Most of that coming from the seat back and the spare.

The TDI with a manual can be a fun, sporty car and still return much better than average mpg.

[COcyclist]

I have a couple more tips, some obvious and one debatable one.

1. Never put roof racks on your car (unless you have to). The roof of the car is in some of the fastest air flow and adding a roof rack adds to frontal area and disrupts what should be an area of attached flow. Putting bikes up there just makes it worse. Some people leave cargo boxes on the roof racks or even deflectors to get rid of the wind noise. The wind noise is turbulence and drag making its presence known. Take them all off!

If you have to pick up some lumber or carry a ladder across town, roof racks make a lot of sense, just remove them when you are done.

2. Carrying a bike on a rear bike racks add drag. I will add a rear rack if I am meeting a friend to go biking but I drive to his house with my bike inside.

Now the debatable one...

3. Get a trailer hitch? I have a small receiver hitch that I mostly use for a 2 bike rack. The rack folds compactly when not in use but can carry a bike for myself and a passenger. Back to the double the per passenger mpg argument. Effective per person 100 mpg.