What Engine LOD is Best for Fuel Economy?

[jime]

Now that many of us have either a Scangauge or a OBDII C&C we can monitor the engine load (usually displayed as LOD). I strongly suspect that the best fuel economy is achieved by staying out of assist, but that leaves a fairly broad range of acceleration rates from stop.

Has anyone done any testing, reading, or research that would indicate the most efficient acceleration LOD in terms of fuel economy (i.e. MPG)?

I know that BSFC charts exist for all engines, but I do not believe anyone has found one for the MT Gen 1. Such a chart would indicate the most fuel efficient load for BMEP(proxy for power), but that doesn't seem the same as fuel efficient acceleration to me. Comments?

[Eli]

0.

Well, we have an Instantaneous Fuel Consumption Display. I don't really pay any attention to load, the iFCD is all you need to watch overall.

I bet IamIan will have something better to say though.

http://ecomodder.com/wiki/index.php/...a_Insight_1.0L

IamIan says this in another thread:

The BSFC chart for the non-Lean Burn state of the I1 ICE puts the highest tiny ~38% efficiency point just bellow 4,000 RPMs ... in non-lean burn and ~3,000 RPMs the best you can hope for would be ~35% ICE efficiency.

Lean Burn is significantly more efficient than just about any non-Lean Burn state for conversion of chemical energy of the gasoline into mechanical energy to move the car ... no matter what RPM or load you are at.

Sounds good to me.

[Cobb]

For max mpg I would agree with the 3x% range of load. I know on the i2 it starts to up shift when you approach 80% load and seems to keep the motor in that range as the going gets tough and the mpg dips.

I wonder if the cvt was shifted to keep the load at the 30%s if that would keep the supreme mpg?

Having said that, that seems to be in reverse to what the graph says about load vs mpg.

Now a variable not mentioned is MAP. I see when the i2 enters what appears to be 150mpg or what some ave called lean burn on the instant read out that the map is about 3-4. When the mpg is in the 50s its reading 8-9 and when stopped at a stop light with brakes on its 14 or so.


Sent from my Autoguide iPod touch app

[Eli]

...

Load is calculated from MAP. Load is just Current Air Flow divided by Maximum Air Flow.

This is calculated by MAP, RPM, barometric pressure and intake air temperature, along with constants like engine displacement and known volumetric efficiency.

[3-Wheeler]

Jim,

For me, the best fuel economy is running at about 34 mph in fifth gear on flat ground with no wind.

In my testing, lean burn starts at 32 mph, and not as low as 28 mph as one other person has mentioned.

Running at 32 mph does not seem to give the best MPG's however. It actually seems closer to 34 or so based on my own testing.

In colder weather like we have now, the best mileage could be at a speed of 36 or so.

I am not running any sort of hot intake runner at this time, so this *may* make a difference, but I just don't know for sure.

I do a lot of FASing, and that really adds to the economy, especially in the warmer months. Much more than any other mod in my opinion.

Probably the biggest improvement to economy is the driver!

Jim.

[diamondlarry]

Awhile back either on another forum, somebody did some testing on a Civic with a Scanguage using the new data-capture feature, and he found that 90% load gave the best economy. He tested several different load values starting around the 70% level. He used the same speed range and gear for each % and did multiple runs at each % then compared the total amount of fuel burned. If I recall correctly, it was a fairly narrow window and as little as around 5% either direction saw decreased efficiency. I'll start jogging the brain cells and see if I can remember where I seen it and get a link in case anyone wants to see the info.

[Need4Speed]

I thought that years ago I read that an engine is the most fuel efficient at a very high load. Makes me wonder if you floor it, then FAS, would that work?

[jime]

Originally Posted by Need4Speed

I thought that years ago I read that an engine is the most fuel efficient at a very high load. Makes me wonder if you floor it, then FAS, would that work?

Yes, I think something like that is where the truth lies. This technique is the essence of pulse and glide, as I understand it. I don't practice P&G so I have no direct knowledge.

The essence of the BSFC chart is that it purports to show the most efficient load in terms of BMEP and RPM. Since BMEP is directly related to engine power, then one would think that exercising very high BSFC over the shortest time, i.e. accelerate hard, at the optimum RPM range, would be the most efficient way to get up to speed. But, the real answer is probably slightly different.

It should be noted that this line of reasoning runs contrary to the thinking of many hypermilers

[AbCaRed00]

Originally Posted by jime

Has anyone done any testing, reading, or research that would indicate the most efficient acceleration LOD in terms of fuel economy (i.e. MPG)?

I think it has more to do with throttle position, but I watched Load after seeing the isobar chart featuring load, rpm and fuel some time after getting the car. I attempted to drive my Insight at around 65% Load at 50mph/80kph cruise monitored on the Scangauge to attempt to achieve best mileage and stay in the lean burn range. Got my best mileages then around that moderate load range by really soft peddling the throttle on long trips and cruising around 80kph to obtain a low load. No doubts wind likely helped out a lot that day.
It works to maintain Lean Burn to keep the Load moderate, but keeping low TPS changes is more direct and relevant.
At that time I also attempted driving with as little assist too on acceleration which meant low TPS numbers as well and trying to keep the percent opening below a TPS of 30. [fwiw: I have recently seen lean burn as high as '32' with warm air intake ducting, even in -10C ambient conditions. IAT=20C with ducting]

In an 8 page SAE paper discussing the engineering details of the Insight, reference is made to load conditions and lean burn once; the key to lean burn appears to be the TPS value in moderate load conditions:

" 5.4. ACHIEVING LEAN BURN ENGINE OPERATION –
Assist from the electric motor, based upon the throttle opening, creates quite linear torque characteristics. This, in turn, improves driveability. In addition, motor assist is also provided under moderate load conditions to broaden the lean-burn operating range, bringing out the full potential of the newly developed lean burn engine."

Source: SAE TECHNICAL PAPER SERIES 2000-01-2216
Development of Integrated Motor Assist Hybrid System: Development of the ‘Insight’, a Personal Hybrid Coupe
Kaoru Aoki, Shigetaka Kuroda, Shigemasa Kajiwara, Hiromitsu Sato and Yoshio Yamamoto. Honda R&D Co.,Ltd.

The MIMA, OBDIICC, PHEV, FAS and other additions will no doubt enhance the aspirations of the car's developers and vehicle owners for years to come.
With the advent of the aforementioned devices and ability to use data logging capabilities the future looks bright for the first gen Insights so equipped.

There are some Insight specific technical papers cited as references at the end of the paper that may be of interest.

[3-Wheeler]

Originally Posted by jime

....Since BMEP is directly related to engine power, then one would think that exercising very high BSFC over the shortest time, i.e. accelerate hard, at the optimum RPM range, would be the most efficient way to get up to speed. But, the real answer is probably slightly different.....

Jim,

Sometimes it is very desirable to take an idea to extremes, and then hopefully discover what negative effects come about based on this thinking.

In our case, we are apparently talking about determining the best way to "pulse and glide".

There two extremes that seem like candidates for our purpose: 1) Take off slowly up to our maximum speed, and then shut off the engine and coast back down to a mininum speed. 2) Take off quickly, and then again, coast down.

Extreme Test #1 - Take off slowly
We are on flat ground, on a relatively deserted road, and we are accelerating at a TPS of let's say 17 or so. At this rate it will take us probably a mile to accelerate up to our maximum speed of 35 mph. We are currently in lean burn and getting more than 75 mpg over this one mile stretch.

Extreme Test #2 - Take off quickly
This example is not exactly realistic, but *if* we took off as fast as a dragster, we would go from 10 mph to 35 mph in 0.4 seconds and burn 1/4 gallon of gasoline during this time.

Extreme Test #3 - Take off not quite so quickly
If we decide to use about 2/3 throttle to get up to speed quickly, there are several factors that affect our resultant economy:

- at the right throttle position, we are at the maximal BSFC of the engine, we are burning fuel more efficiently, but we are still burning more fuel because of the throttle position. We are putting more energy into accelerating the car at a higher rate.
- this higher acceleration also is known to take more hp, which requires more fuel, and so on.
- taking off more slowly lowers the required acceleration, which in turn burns less fuel. Maybe not as efficiently, but still less fuel.
- there is most certainly an optimum where we accelerate the car up to a desired speed that uses the least amount of fuel and keeps acceleration to a minimum as well.

I have no idea where this optimum is right now. Obviously every serious eco-driver is looking for this same optimum point.

If I had a patch of road that was flat and straight for let's say five miles, and little traffic, it would be very interesting to perform a series of tests to find this optimum for the purpose of pulse and glide driving.

Jim.