P&G freeway tested ABAB +14% FE

[Arragonis]

I only tried EO(ff)C a couple of times in the Fabia but I used the the key to restart. I was probably over worrying about the clutch but it cost me £1200 to replace the other year. I stuck to EO(n)C instead mainly as I wanted to retain the PAS (with the engine off the Fabia was a pig to steer) and also because I was worried about heat-soak in the turbo causing the seals to fail.

Now I don't have a turbo so I may try that more, also the steering on the Aygo is dead easy with the engine off - I don't start it for rolling the car round the drive unless I need to move it up the hill.

[larrybuck]

To California98Civic and others!

It sounds like you have really GREAT GAME going on, but I was curious because I believe you mentioned that these substantial uphills are all on a freeway.

Wouldn't it be prudent on a long uphill stretch to tuck in behind a heavily loaded truck, and just putter up the hill at a relaxed constant speed?

Are the police that mean about STEEP HILLS? With the vintage of your car, wouldn't "It's a little tired, I'm trying to make it last in this economy" work IF you were stopped?


I never drive any faster than I absolutely have to!!!

[Fat Charlie]

Well, California98Civic clinically proved that while P&G isn't the best way to go up long hills, it still beats cruise. On his car, by 14%.

d0sitmatr- how much gas is left when your empty light goes on?

[PaleMelanesian]

I haven't done an ABAB test, but I have proven to myself many times over that P&G is best even climbing hills. (manual trans) I run at 80% load at all times. If that means I'm accelerating up the hill, then I do a (short) glide and then get back on the gas at 80%. That's more efficient than steady speed at 60% load. If the climb requires 80% load to maintain speed, that's still at maximum efficiency and I just call it one giant pulse.

[toc]

How is load determined?
I take it 80% load is not 80% Throttle ?

[California98Civic]

Originally Posted by larrybuck

Wouldn't it be prudent on a long uphill stretch to tuck in behind a heavily loaded truck, and just putter up the hill at a relaxed constant speed?

Are the police that mean about STEEP HILLS? With the vintage of your car, wouldn't "It's a little tired, I'm trying to make it last in this economy" work IF you were stopped?

Hiya larrybuck. Thanks for the comment, hey. I agree about drafting. But this was a test of this one technique, so I had to control for it as best as I could. Drafting is reliant on the luck of getting the right situation. But yesterday I drafted a truck across a 22 mile all-freeway route (smaller hilly % than the test route) and pulled 73.2mpg at an ave 53.5mph. Last week on that route without drafting: 63.3 @ 59.4 ave mph. BTW, I don't follow very closely. Three or four car lengths is my favorite because it discourages people getting in between and seems to be as good or better than hyper close, according to Hucho's aerodynamics book.

On the puttering up a hill at a slow constant speed question. First, yes, the police will pull you over at 40 or 45 mph, and technically could any time you fall below 55. Freeways here are six lanes across in each direction and people drive 65-85 routinely. You can get killed. The slow speed would also be a mistake, probably, from an efficiency standpoint, even while drafting. Your car will operate relatively inefficiently at low load% and burn more fuel over the same terrain. I know it sounds wrong. But if you follow your gauge to appropriate high load for your motor, you can drive a little faster (saffer and more legal) and get a lot higher FE and you don't have to EOC on the freeway. But if I were to do what you describe, I would vary my speed, seeking an average that keeps me steadily behind the truck, while allowing P&G with load ("GLEN") so I can get higher load% averages out of the engine for greater FE.

As for the vintage of my car... I hear you, but "this is the ship that made the Kessle run in 5 parsecs... she's fast enough..." I've been dodging the empire for decades.

[euromodder]

Originally Posted by toc

How is load determined?
I take it 80% load is not 80% Throttle ?

That's right.
It's 80% of the work the engine can do - as seen on an OBD tool like the ScanGauge or Ultragauge.

With my diesel I can be at 95+ % load with the accelerator pressed down less than 1/4th.
Pushing it down further doesn't help once beyond 98%.
It just tries to add more fuel.

[PaleMelanesian]

80% load comes from a Scangauge or Ultragauge. It's in the 33-50% throttle range at these low rpms.

[Piwoslaw]

On my way out to vacation I got a chance to do ~90km on the highway in relatively flat terrain (we usually go to the mountains, so most of my long distance driving is rolling and hilly terrain). It was not a pool table, but pretty close, it was much flatter than anything I've driven on in the last few years. I decided to use this chance to check the efficiency difference between steady, cruise control driving and PNG (P&G in Neutral, ie with engine on).

Since this came up at the spur of the moment, the test is not exactly ideal. The only thing I could come up with was to watch the engine coolant's temperature as a measure of efficiency. The outside temperature was ~21°C (68°F) with a strong side wind. I had my radiator's lower grille blocked (upper grille and intercooler were unblocked). Each try lasted at least 5-6 km (3-4 mi) to allow everything to stablize.

• Driving on CC at a steady 95 km/h (59 mph) leveled the coolant temp at 92°C (198°F),
• Driving on CC at a steady 90 km/h (56 mph) gave 91°C (196°F),
• Pulsing to 100-105 km/h, then engine-on coasting to 80-90 km/h quickly brought the temp down to 86°C (187°F), and after a while to 84°C (183°F)

During vacation I planned ahead so that on the way back I could do a better test. This time I made sure the distances were the same on each try and I used the car's OBC to measure fuel consumption and average speed. I tried to make sure that average speed during PNG was the same as the set CC speed in the previous run. Unfortunately, I wasn't able to do as many tests as I had planned - during the fourth run our infant son started crying and I had to make an emergency stop for an hour
Outdoor temperature was 32°C (90°F) with a headwind, lower grille block open. Tests #1-3 were 12 km (7.5 mi), test #4 was 8 km (5 mi).

1. Cruise control at 94 km/h (59 mph), engine load 40-60%, consumption 3.5 l/100km (67 mpg), coolant temp 81°C (178°F),
2. Pulsing to 105 km/h (66 mph), engine-on coasting to 85 km/h (53 mph), average speed 94 km/h (59 mph), engine load ~80% while pulsing and ~25% while idling, consumption 3.1 l/100km (76 mpg), coolant temp 79°C (174°F),
3. CC at 90 km/h (56 mph), consumption 3.4 l/100km (69 mpg), coolant temp 82°C (180°F),
4. PNG between 80-100 km/h (50-63 mph), average speed 90 km/h (56 mph), consumption 3.4 l/100km (69 mpg), coolant temp 81°C (178°F).

NOTE As I found out during the tests, #3 was slightly downhill towards a large river and #4 was climbing back out of that river basin. This explains why PNG had the same average fuel consumption as CC at the same avg speed.

Summing up, of all of those tests only #1 and #2 on the return trip are anywhere close to ideal tests. They imply that driving at a steady 94 km/h consumes 13% more fuel than PNG between 80-100 km/h with the same average speed. Again, this was in flat terrain during hot weather.
This means that PNG is still efficient on flat roads at highway speeds up to 100 km/h. Since the speed limit on this highway was 140 km/h I could have tried to find the break even point, but that wouldn't have been fun, since I don't like going that fast. My guess is that CC starts to take over when the engine is at constant 80% load, assuming that gearing allows rpms to stay in the ideal range for best BSFC. In rolling and hilly terrain I'm sure that PNG would allow better performance, since it would be possible for the driver to syncronise pulses and glides with hills.

As a side note, please praise me for going at only 2/3 of the PSL

[MPGranger]

Originally Posted by California98Civic

As for the vintage of my car... I hear you, but "this is the ship that made the Kessle run in 5 parsecs... she's fast enough..." I've been dodging the empire for decades.

Umm... Han? Isn't a parsec a unit of distance, not time?