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Old 04-29-2012, 09:16 AM   #1 (permalink)
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New here, ... the physics of hypermiling?

(reposted from CleanMPG...)

I've started hypermiling in my '93 Mitsubishi Expo LRV, 1.8 L 4G93 SOHC 8-valve engine. Multiport Fuel Injection. No instrumentation (yet, can't decide). Just fixed the speedometer cable, broken for years. Hey, it runs great without it! (Money is tight)

I'm new to all this, looking at a lot of information about FE , etc. but I'm coming to a few simplifications to understand hypermiling. Tell me if this is right. (I was a physic major so... it guides my thinking).

Basically, I'll get the best mileage if I either have the ICE off, in a coast (or because I took my bike!). Or, I'm operating at minimum BSFC, probably rapidly converting gas energy to kinetic energy (accelerating for later coast) since all cars are in a sense highly overpowered. Guessing thats somewhere at 75% throttle, 2000 rpm. We have a sledge hammer to drive a tack. The big trick is then not getting arrested, killed by road rage, crashing, or having to hit the brakes wasting that kinetic energy. But last night I came all the way home without touching the brakes. I mostly bump start, brief pulse at high throttle about 3-5 sec, ICE off, long coast. No idea of my mileage.

Other FE effects: weather, choice of route, managing engine warm-up costs, good maintenance, having "efficient hardware" to start with (your choice of car: engine, aerodynamics, rolling resistance).

There's a question of choice of gear and average speed (in theory always running at minimum BSFC), but that's kind of a trade-off of time to destination .vs. fuel used (i.e. time is money) because wind drag increases with (the square) of speed. We decide how much our time is worth .vs. fuel. Also, there's limited gear choices and manual or automatic control.

Where is the minimum BSFC operating point (s)? It seems it would be helpful to have a procedure to map this out practically, then instruments to tell me where I'm at, say with a bar for rpm and throttle position, above or below exact minimum. Rather, it seems most people "hunt" for it with data clouded with all other effects, tracking instantaneous and averages of FE. I'm confused what instrumentation to get. I'll post separately all that.

In general, what features, describe an (market available or not) car best for Pulse and Glide as I describe it? (apart from "efficient hardware") A manual transmission with kill switch? Or turning key-in-ignition Fas ? Some make/model hybrid? What size engine would it have? Once you completely put your driving behavior on the table to the point of advanced Hypermiling techniques, it seems current hybrids are not quite right. They're better for people who don't want to change driving behavior (so much). Or think about it. Of course, the "efficient hardware" tends to be in hybrids though.


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