“Be kind, for everyone you meet is fighting a hard battle” - Often attributed to Plato but likely from Ian McLaren (pseudonym of Reverend John Watson)

Sunday, September 30, 2012

CT200h fuel economy summary

I've been driving the Lexus CT200h for about 14 months. In that time, I've used 474 gallons of unleaded regular grade fuel and driven 24,372 miles, thus realizing an aggregate fuel economy of 51.4 m.p.g. The maximum I've achieved on a tank full is 54.7 m.p.g., and the minimum is 45.7 m.p.g. The standard deviation of my m.p.g. for each tank full (not weighted by distance driven on that tank) is 1.99 m.p.g.

The graph below shows my mileage history. Click on it for a larger view.

Thursday, September 27, 2012

Faulty comparison?

I follow (and link to) a fair number of energy related blogs. One of them is Consumer Energy Report, which aggregates posts from a variety of journalists and energy professionals with various specializations. A recent post was entitled "High Cost Prevents Electric Cars From Penetrating the Market." In this post, Andrew Holland discusses his thinking behind the lack of sales of pure electric cars and the financial troubles befalling some of their manufacturers. However, he's also quite complementary of the Chevy Volt, a vehicle I've considered.

But in the comment section, Buddy says

I’ve also never understood, however, how I can run a 5K Honda generator for a minimum of 2 hours ,and occasionally 4 hrs, on a single gallon of gas, that hybrid vehicles cannot achieve the 100 MPG rate easily.

Is this a valid comparison? After all, I certainly can't drive my hybrid  Lexus CT200h for 2, let alone 4 hours on a single gallon of gas. I think looking at Buddy's comment with the Lexus as the representative is quite reasonable. It's the same drive train as the ubiquitous and iconic Prius hybrid and I've gotten 51.38 miles per gallon total in the 14 months or so that I've driven it.

I wrote a simple Wolfram Mathematica program to determine an estimate for the power required at an input speed and an estimate for the mileage to be expected. The program comes gratifyingly close to my actual mileage at the speeds I've checked so I suspect that the power requirement is likely pretty close, the wild card being the engine efficiency.

In any case, let's go on. Buddy's Honda generator has a maximum rated output of 5 kilowatts, but I'm very doubtful that the two hours to which he refers is at full load. Nevertheless, I'll use it anyway because... who knows? And I suspect the two hour figure is at closer to full load while the four hour figure is at a much lesser load.

5 kilowatts is 6.71 horsepower. I calculated that, at 55 m.p.h., my Lexus requires from its Atkinson cycle internal combustion engine (and, where required, the generator and electric motor) about 13.8 horsepower and achieves about 54 m.p.g. If I assume that, at that cruising speed, the Lexus is capable of 28% efficiency, then I'd be burning fuel to release heat energy at the rate of 13.8/.28=46.4 horsepower. This is 34.6 kilowatts or 34,600 joules per second. Now, upon burning, a gallon of gasoline releases about 120,000,000 joules of heat energy so this gallon should last 3,470 seconds or just shy of 58 minutes. A quick check: at 54 m.p.g. and 55 m.p.h., a gallon ought to last an hour!

OK, so we have that I need 13.8 horsepower, a bit over twice what Buddy's generator supplies at 5 kilowatts or 6.7 horsepower. Multiplying my one hour by that 2 figure, I'd think his generator should run for about 2 hours at 5 kilowatts if it was as efficient as my Lexus. I don't think there's any reason for Buddy to be surprised!

Wednesday, September 26, 2012

Long ago in a galaxy far, far away...

In a book entitled "The Positive Philosophy," French philosopher Auguste Comte, writing about the unknowable, said of the stars "we can never learn their internal constitution, nor, in regard to some of them, how heat is absorbed by their atmosphere." Of course, very shortly thereafter, the spectrograph (or spectroscope, spectrometer, or spectrophotometer) was turned to the heavens and the rate at which we learned the inner workings of stars and, soon thereafter, galaxies was truly amazing.

We can now look back about 96% of the way to the beginning of the universe (some 14 billion years ago). How do we look back? It's because light, travelling at 300 million meters per second (186,000 miles per second) takes a finite amount of time to reach us. If we look at something a light year away, we're seeing it as it was a year ago.

Instruments on the Hubble Space Telescope were used to create the image above, now the deepest look into space ever, showing galaxies formed at the very beginning of the star forming phase of the Universe's evolution. You can read about the instruments and methods that allowed us to look at this truly incredible view of our Universe here.

Note: I am currently working at moving my blog from Blogger, with its limitations, to a Wordpress self-hosted site. I'm hoping for a smooth transition with all comments, links, graphics, etc. intact and even search engine continuity. We shall see.

Sunday, September 09, 2012

A (kilo)calorie quickie

I've been in "downsizing" mode and have been on a reasonably rigorous workout regimen. As is my wont, I've adopted some technology assists and, in particular, utilize a couple of iPhone apps. One of the ones I use on days when I run is called "Runmeter" by abvio. It uses the GPS in the iPhone to yield distance, time, pace, altitude gain and loss, and others. It exports my path to Google Maps as well. If I select, it will Tweet my run and people can follow me and, when they tweet replies, it will speak them to me. I don't use this option though.

To the point of this post, once weight is entered into the program, it tells calories used (of course, these food calories are really kilocalories) and time. This can be converted to average power used during the run. it's as simple as plugging "471*kilocalories/(2287*seconds) in watts" into Google search bar. Unfortunately, the resulting number, about 860 watts, seems highly implausible if not downright ridiculous. That's over one horsepower for 38 minutes, and I'm no world class athlete. I'm hardly a neighborhood class athlete! Perhaps it's calculating the total, including my base metabolism of about 100 watts. That would make the increment of the running 760 watts or right at one horsepower. Also not possible.

And yet I've read that very strenuous physical exertion can burn on the order of 600 kilocalories/hour. This is just shy of 700 watts. On the other hand, many sources say that world class athletes can produce 1000 watts very briefly and a much smaller number for any significant length of time. For example, the graph at left shows the continuous power production of Masters Men (35-39) Hour Record holder (bicycle) Jayson Austin's rides in 2008 and 2009 (click to enbiggen). In 2009 his average power output over the hour was 302 watts.

I think that there's not much question that there's a problem here someplace! My suspicion is that the athlete figures are "external work" only, i.e., force exerted against the environment times speed. Then, the "food energy burned" figures count that as well as the internal energy burned to produce that work. If this is the case then, if I knew my rate of performing external work, what I'll call "athletic power," then I could use that and the internal metabolic power to calculate my efficiency of energy utilization. In my cycle of rotation of exercise, one of my workouts is a bicycle ride. One can get a "power meter" to measure actual athletic power. I'll post results when I get them.

This actually is pertinent to me as another iPhone app, Lose It, tracks my weight loss progress. In it, I log my food intake (it scans barcodes and has an extensive list of foods plus the ability to create your own foods and recipes) and my exercise calories to predict when I will reach my goal weight. Its evaluation of my exercise is similar to the output of the run meter when I plug in my weight, exercise type, and pace. It also tells me, based on my desired kilocalorie deficit (the difference between my daily "burn" and my intake), how many kilocalories I have left to eat on a given day. If my exercise kilocalories burned are less than the apps indicate, I may be eating more than I should given my desired deficit. On the other hand, the weight loss progress is good so I don't think I'll modify the inputs.