MAF reading g/s

grams per second seems to be the answer, though why, rather than a volume is unclear, perhaps because of the density of air changing with temperature?

I guess the clue is in the name, Mass Air Flow detector. It's the "mass" of air passing it that is measured by heat dissipation from the element. Thinner air will remove less heat even though it has the same volume. Being thinner, it requires less fuelling.

Tim

Here's the problem though. The lambda sensor will be mandating an air fuel ratio of 14.7 which means 1.17 grams of fuel per second. That's 4.2 kg/hr or

9.3 lbs/hr which is nearly 1.25 gallons per hour. Now a car travelling at a steady 50 mph and achieving 40 mpg is also burning 1.25 gallons of fuel per hour and a car at tickover can't be burning anywhere near that much. From people's readings from fuel consumption sensors in modern cars about 0.2 to 0.3 gallons per hour at tickover is more like it. So that air mass reading is 4 or more times higher than possible if it's in grams/second.

I found this while hunting around: "for the 3RZ motor they are 2.6 - 3.7 gm/sec at idle and 9.2 - 13.3 gm/sec at 2,500 rpm without load" That is a fairly big engine and shows the logically right figure as Dave described.

So the OP getting 17 odd, maybe a factor of ten out?

Thanks, yes it could well be the Autel firmware misinterpreting the number.

What I do know is that I occasionally get a low MAF reading OBD fault code generated and if I switch on my Synergy's MAF compensation, the fault is never generated.

Switch off generates figures in the 14 g/s range Switch on generates figures in the 17 g/s range

You have to be a bit careful with the assumptions about the optimum sized engine for a range extender. If you look at the charts of BSFC for engines most produce their lowest BSFC at about or just under half of peak rpm and about 80% throttle. That works out to be about 35-40% of the peak bhp output. For example.

This implies that to generate 30-40 bhp you want an 80 bhp engine to operate it in its best BSFC range.

However, and it's a big but, a smaller engine operating at a higher percentage of its peak output might not be in its best BSFC range but due to lower frictional losses might still have a better BSFC than the larger engine. Or it might not as smaller engines tend to be less thermally efficient than larger ones. The only way to be sure is to pick the engine with the best BSFC at the target output regardless of engine size or peak output. Regardless of other considerations that pretty much mandates a diesel rather than a petrol to start with.

For many years now I've been working on the problem of designing the most fuel efficient vehicle with the help of various spreadsheets I've written to calculate road load bhp from drag and vehicle mass data and turn that into mpg using BSFC assumptions. I'd be happy to share the equations if you want to write your own version.

When bringing electric vehicles or hybrids into the equation I see a number of options. Pure electric vehicles have very limited range and long battery recharge times. No use for long trips. So how best to design a hybrid?

If you design in a long range on electric power only the battery mass, volume and cost has to be high. If you design an optimum fuel economy vehicle with only a small efficient diesel engine the performance is low. A solution might be a hybrid with a "shopping" range electric battery pack, say 30 miles only and an 80 bhp motor plus a 20-25 bhp diesel engine for long trips.

A vehicle with 16 sq ft frontal area, 0.26 Cd, 0.011 rolling resistance and

1800 lbs weight would only require 16 bhp to cruise at 70 mph. At a BSFC of 0.35 from a small diesel engine that would give over 100 mpg at 70 mph. For acceleration the electric engine kicks in to give the full 100 bhp. A bit like KERS in F1 cars. For short trips you use electric power only and recharge from the mains overnight for the cheapest possible motoring. For long trips the system cruises on diesel and keeps the batteries charged at 25% to kick in only when needed. You plug the batteries in to charge back to 100% more cheaply from the mains when the journey is over.

With regenerative braking to charge the batteries in stop start motoring you could avoid diesel use for most short journeys but still have unlimited range for long ones from the fuel tank and petrol stations.

For my own use which consists of mainly 20 mile shopping trips with the occasional 500 mile holiday one it would be ideal. The same performance as my Focus but three times the mpg on long trips and almost zero cost on short ones.

With such a limited electric range you could manage with conventional and cheap lead acid batteries - about 8 to 10 of them at 15 kg each and £500 instead of the many thousands of pounds for Ni hybrid batteries.

Thoughts welcome.