The AX Eco Project : 100 mpg target !
 

Hello everybody,

So, this thread is the continuation of my presentation thread I started last year but with all the technical about my mods.
http://ecomodder.com/forum/showthrea...e-16767-2.html

I called this project "AX Eco", inspired by the prototype that was presented in 1994 by Citroën. The car's mileage was 87,1 mpg at 56 mph (2,7 l at 90 km/h) compared to the production car's figure of 71,3 mpg (3,3 l). I have the post 1994 version which comes out at 65,4 mpg (3,6 l), a bit more than the previous version but due to its major cooling problems leading to head gasket issues, that version was a no-go for me.

The target is to get 90 mpg at 56 mph (2,6 l at 90 km/h), so a bit better than the prototype. If I reach this, it will mean 100+ mpg at 40/50 mph speeds (2,35 l at 70 km/h). Every mod will be translated into a modification of the weigh/CdA/Crr/engine efficiency datas to calculate the theoritical FE at 56 mph. I know this method will not be completely accurate : when I my make a mod the car produces less power and torque (rpm is equal) so the BSFC changes a bit (in the wrong way at low load). But whatever...

I have driven 30.000 miles so far at 77,1 mpg average with a few mods already done.

Here are the official datas (except the Cr I measured experimentally) of the stock car.

Weigh : 805 kg (1777 lbs), + 80 kg for driver and fuel
Cd : 0,31
A : 1,74 m² (18,85 ft²)
CdA : 0,5394 m² (5,844 ft²)
Crr : 0,0109 (Michelin E3B 155/70 R13 at recommended pressure 31,9 PSI)
Engine efficiency : 22,7% (determined with above datas and official FE)

Measuring fuel flows
The car has an old diesel engine with no electronic whatsoever. I looked into flowmeter systems like heating oil counters but these were very expensive and I had no remote display. After some searching, I heard of the Zemco system. I grabbed 2 of these, two because I have a return line to the tank. I have yet to receive the second one. I won't have direct display of the consumption but consumptions of each line which I'll have to substract.
My mods will be measured bidirectionnally on a 28-mile distance part of my 43-mile commuting trip at 56 mph constant speed.

Tires
For now, I just hyperinflated the tires to the max. sidewall pressure : 44 PSI. Crr drops from 0,0109 to 0,0095.
Measured on a flat road with no wind. 5 measures in each direction for each pressure. Results were 42,17 seconds to coastdown from 16,5 km/h (actual speed when my speedo is at 20) to a complete stop at 31,9 PSI and 48,21 seconds at 44 PSI. Despite being low, my calculations also take into account aero drag (neglect it will slightly overestimate Crr).

Weight
Not much here. I removed all the seats I don't need. I always drive alone and I also need the space to carry stuff from time to time. 63 lbs gain.

Aero
The mods I have already done are :
-Radio antenna removal
-Right mirror removal
-Front wiper removal (in the car)
-Sealed front gaps
-Partial grill block
-Rear wheel skirts

I calculated the theoretical gain of the radio antenna by multiplicating the measured frontal surface by the drag coefficient of a cylinder. CdA drops by 0,0012 (0,14% better FE).

As for the other mods I will probably measure all together (maybe both fuel flow measurements and coastdown tests to compare) because the effect of each alone is too small.

New data with mods measured so far :
Weigh : 1714 lbs
Cd : 0,31
A : 1,74 m²
CdA : 0,5383
Crr : 0,0095
Engine efficiency : 22,7%

FE at 90 km/h : 3,42 l/100 km (68,8 mpg)

My next (major) mod will be changing the 5th gear ratio. By the end of the year, I hope.

Wow, you're really off to a good start:thumbup:

I googled the AX Eco and at first glance the only external differences are smooth wheel covers and a short Kammback. There may also be an undertray, but I haven't found any info on that. These aeromods drop the Cd from your AX's 0.31 to 0.28. Weight is just under 700kg. It had the older 1.4 (1361 cm3) diesel, no info as to whether it was tuned. It's fuel consumption of 2.8-3.4 l/100km is what you are already getting, so you are heading in the right direction.

Smooth hubcaps, an undertray, rear wheel skirts, and a Kammback extending to the rear bumper should get your Cd down to 0.28 or even lower. I'm not sure how you can reduce the weight to 700kg:confused:

How much can you cover you grille? Is your present grille block the max you can do without overheating? Maybe an openable version for quicker warmup? You need not switch to 165-width tires, Continental makes 155/80R13 EcoContacts, which are standard in the eco versions of the Opel Corsa.

Congratulations on the good numbers !

We want pictures !

Alternator delete can be a worthwhile option if there is no issue with the water pump.

Also, car manufacturers are working quite a lot on reducing warmup time, maybe that's something you can consider ?

Thanks for the support !

I have some documentation on the AX Eco. The engine was tuned, but they don't tell what. The car had also side skirts, a front dam, smaller mirrors, sealed light gaps and 155/70 R14 tires.

Undertray and kammback are planned. As for the weight, if I stick only to removals (free) I could cut 70 kg by going extrem (dashboard, door covers, carpet, spare wheel). But I don't plan to do much on weight. I think I can do as good as the proto with a heavier car.

I have the upper grill always blocked and lower grill fully opened in summer and half opened in winter. I live in a rather warm region, I can't close it too much. We have 15°C in winter and 30-35°C in summer.

155/80 R13 is only Ecocontact 3 and the new Ecocontact 5 is apparently much better. Moreover, I will gain 7% on the gearing by switching to 165/70 R14. Many green tires should be released in 2013. I will take the time to make the good choice since my current tires are only half used.

Alternator delete seems like something inconveniencing. That means you have to recharge the battery everyday ?

Yes. Plus you should change to a deep cycle battery, learn to monitor the battery charge level, know your electrical consumption, and be able to calculate how far you can safely drive on the battery.

A solar panel on the roof could eliminate regular charging.

Not as good FE-wise, but much more practical, is an alternator kill switch. You disable and enable the alt's field wire at will, for example the last few kilometers before home (where you can top off the battery), or turn it off when idling and on when engine braking, getting a charge for free.

You still have some losses, since the alternator and its belt add a small load to the engine, but you reduce the electrical load to zero whenever you want. And since your car doesn't have any electronics, then the constant switching between 12V and 14.5V shouldn't be a problem.

has anyone in any vehicle considered and modified the cooling set up, eg faster flow rate of coolant, bigger capacity of coolant, more efficient radiator type,?
would changing temp sensitive valve help cooling too?
what about manual operated fans so can change at will?

I have no experience myself but live in much cooler climate, so only heating problems for me are in traffic.
hope you get some good ideas from all that.

Temperature management these days as I know it seek to heat rapidly and then be able to properly cool the engine.

For example, you use your faster heating water to heat up oil and then revert to cooling it.

An engine is more efficient when it is quite hot but the cooling has some sort of lag so it is always a compromise.
Also more efficient cooling means more water / bigger radiator and so on so you get more "cooling lag" and more weight too ...

Honestly I can't really figure out what can be done to such good numbers.

Maybe some kammback of the rear end ?

I have more than one trick up my sleeve. I won't reveal all at once. ;) It's a long-run target, though. Maybe 2014.
I'm waiting for my second flowsensor and then I'll be able to do the 5th gear swap with the mpg test.
I'll make a kammback, yes. But only partial, not longer than the bumper. The shortness of the car is an advantage I want to keep. I have already studied the framing and the material of the kammback.

I had the technical inspection (every two years) of my car and I have a few things to do so it can pass. I have some play in a rear wheel, the swingarm's bearings must be replaced. At nearly 300.000 km, that's something normal on that car. Good thing is that on these cars everything can be fixed for cheap when you do it yourself.
So my longer 5th gear mod will have to wait a bit. :(
Also, for the inspection I removed all the mods. And wow, I saw my consumption rise to 3,3 l (vs 2,8-3,0) although driving very cool like usual.
I didn't imagine I gained that much with the mods since I did them one by one. When you change all at once, you see the difference.