Quote:
Originally Posted by BV1
Similar thread: http://ecomodder.com/forum/showthrea...ate-28617.html
...ideal eco-acceleration should be the maximum acceleration available prior to entering open loop, or pulling ignition timing due to knock, or increasing AFR, in the highest gear possible (or lowest RPM). ...upon reaching the intended speed one immediately starts to Pulse and Glide,... ...gear ratios are locked for a particular gear, so in order to take advantage of the higher efficiency near WOT...
This minimizes frictional losses in the engine by using the piston stroke, valve duration and pumping losses to their maximum ability and since rotational losses are not load dependent the greater power output increases the efficiency of each engine power stroke by reducing the loss %. |
I have two quite different experiences that verfy all this about engine load, rpm's and BSFS-maps:
The first is an experiment started in pure desperation when my little Fiat 127 got a conrod bearing seizure. I brutally ripped out the faulty rod/piston and their closest counter-acting neighbour. I stick-welded the lubrication orifices in the crank and grinded down the corresponding cams. The once 1050cc engine became a 20-25 hp 525cc with 180 degree crank. During the following year I drowe the little car 30.000 realy hard, with a lot of high revs on lower gears to keep the same average speed as before. Despite the hard running I got a 10-15% reduction of fuel consumption. I guess it's a good example of reduced friction and pumping losses, as well as a proof of the benefits of higher load. Driving the car with downsized engine was sometimes a bit scary in the beginning since I was used to engine braking to reduce speed. With only half the engine left it almost felt like the car had a freewheel.
For some time I thought that engine downsizing was the great quickfix to chop off a chunk of fuel costs. The reduced engine power may however be both stressful and even dangerous. The rev-range is also reduced a lot and you cal almost count the piston strokes while driving on low revs. The need of high revs to get the necessary power counteracts some of the fuel savings. So no, engine downsizing is not a perfect quickfix, but it's a quite cool thing to have tried!
Projektblogg - Fiat 127 engine downsizing
A much more rewarding quickfix is to change driving style. -Enter the mighty P&G, Pulse and Glide, or BURN & GLIDE as i prefer to call it! After the little Fiat I have a 1975 Saab 96 V4. Owners of such cars are used to a consumption of about 7-8 L/100km (33mpg). This summer I made around 4,3 L100 (55mpg) again and again, with slightly reduced average speed but extreme use of P&G, or B&G as I prefer to call it. The method is truly about finding the BSFC sweetspot and staying there while the engine is used. If you can't stay within the sweetspot, the engine should be SHUT OFF! I got realy good fuel savings from DWB, Driving Without Brakes, and even more when I introduced B&G. When I finaly introduces engine shut-off I saved even more.
Using B&G with engine shut-off together with DWB is both fun and hard work. It's also extremely annoying to other drivers during rush hour and dense highway traffic. -Use the method responsible! Since it's a very activ driving style you become more aware of other cars and how they interact. Getting skilled with B&G+DWB in city traffic can actually help you get where you want quicker than the average driver! You learn to "read" traffic in a totaly different way. I often pass the same angry BMW several times, making him even angrier, being passed by the same slow and scrappy Saab again and again... -The harder they try, the harder they fall!
I try to avoid revs over 3000. I try to keep the engine around maximum torque at 2500 rpm and perhaps 70-90% of full throttle to avoid carburettor enrichment. I also add about 20-25% ethanol to the fuel. This servers three purposes: Ethanol is cheaper, makes the fuel-air ratio a bit leaner (closer to the carburettor's margin) and prevents pinging, premature ignition and keeps the engine from running backwards (!) every time I shut it off after each heavy burn-cycle. I've also heared that ethanol burns cooler and slower than petrol, which can improve fuel efficiency at lower revs.
High revs are bad because of increased friction and pumping losses, low revs are a bad match between piston speed and heat transfer to the engine block. -Just take a look at a BSFC-map or even a rpm/torque graph and you can clearly see that fuel efficiency is best where the torque is around maximum.