Sunday, March 18, 2018

How efficient is a car?

The Second Law of Thermodynamics puts an upper limit on the efficiency of a heat engine. The most efficient heat engine is a Carnot cycle engine, named after Sadi Carnot, who worked out the  maximum theoretical efficiency of any heat engine. It’s 1- Tc/Th, where Tc is the temperature of the cold side of the engine, and Th is the temperature of the hot side. Heat flows from the hot to the cold side, and on the way some of it can do useful work.

So how much work can a gasoline engine do?

In real life, friction and other factors reduce the efficiency of the engine. Long years of experience with gasoline engines shows that typically they operate at about 25% efficiency. That is, of every 100 litres of fuel you put in your tank, about 25 litres move the car and what’s in it. The other 75 litres are wasted in the form of exhaust gases, friction, heating the engine, etc.

That’s the efficiency of the engine. It’s not the efficiency of the car.

To calculate the efficiency of the car we need to know the total weight of “the car and what’s in it”. You, the driver, are in it.

Let’s say you are a typical Canadian male and weigh about 200 lbs (90kg). A car itself typically weighs about a ton (2000 lbs, or 900kg). Together, you and the car weigh about 2200 lbs, or 1 tonne (1,000kg). So you weigh about 10% of the total.

So only about 10% of those 25 litres that move the car and you actually move you. Or, thinking about the fuel in the tank, out of 100 litres, 2.5 litres are used to move you down the highway.

That means the overall efficiency of the car as a means of transporting its lone driver is 2.5%.
Since fuel costs money, that means of every $10 you spend, 25 cents will pay for your transportation, and the other $9.75 pay for moving the car, wearing down its parts, and heating the air.

You can increase that efficiency. A lighter car is more efficient, because you make up a larger fraction of the total weight. A car loaded with passengers and their gear is also more efficient, for the same reason. A vehicle that carries a lot of passengers and a lot of gear, like a van or a bus, will be even more efficient. However, with just the driver, a van or bus will be less efficient. A pickup truck, which weighs considerably more than a car, will always be less efficient.

From a selfish point of view, one should buy the lightest car one can use, and use it as little as possible. From a social point of view, one should probably not use a car at all, or only when absolutely necessary.

Friday, March 16, 2018

Richard Stein, architect: Energy Conservation n the Building Trades.

Richard Stein was Ethel Stein husband. His obituary includes some interesting calculations about the efficiency of buildings.

Textile Artist Ethel Stein (link to obituary)

Textile as an art medium is of course underrated and often dismissed as mere craft. Ethel Stein is one of many people who have been overlooked for this reason. Which means that I knew nothing about her until I read her obituary. I suppose some would say that's a minor deprivation, but I disagree.

Monday, March 12, 2018

So You Want to Build A Model Railroad... (Mid-sized Trackplan)

      Ian Rice. Mid-sized and Manageable Track Plans. (2003) Rice doesn’t design track plans. He designs layouts. The difference is that a layout has a theme, usually based on a prototype and one or more of its locations. While layouts rarely copy the prototype exactly, a good design will use the tricks of selective compression, key structures, and characteristic landscapes to create a believable impression of a real railroad.
     It’s not much of a trick to arrange track to fit a given space. Many model railroaders do that with actual pieces of track placed on the table or benchwork, which has also been built to fit the space. But whether the trackplan is drawn or sketched on paper or a computer screen, or laid out with actual track, the challenge is to translate the trackplan into a layout. Rice has the gift of visualising the end result, so he includes buildings, scenic elements, and often view blocks to encourage the visitor to see only one scene at a time. His layouts tend to be a string of dioramas.
     Rice also selects a time frame, and describes the locomotives, the traffic, and other components that will fit that time frame. He fits the benchwork to the trackplan, not the other way round. His layouts feature not only sweeping curves of track but sweeping curves of benchwork.
     The layouts shown here fit four standard sizes: a 12ft x12ft bedroom; a 10ft x 16ft corner of a basement; a 10ft x 20ft single garage; and a 20ft x 20ft double garage. Almost all use a 24 inch or larger minimum radius. They are certainly manageable, in time, money, and space. Rice discusses these and other constraints and determiners of model railroad building in the first three chapters, then offers fourteen plans, with accompanying discussion.
     He’s a good writer, if somewhat too fond self-deprecating lame jokes. Anyone who’s starting out in the hobby will find this book useful and inspirational. The model railroader who’s become dissatisfied with what’s been built, and is willing to tear down and modify or even start over, will find this book a good source of ideas to guide the redesign. Recommended. ***½

Wednesday, March 07, 2018

A wheelbarrow of cash for a loaf of bread: The Downfall of Money (F Taylor)

     Frederick Taylor. The Downfall of Money (2013) The story of the German hyper-inflation that followed World War I, 1919-1923. Taylor mixes political, economic, and personal stories, which gave me a vivid impression of what it was like to live through that time. For example, a memory of how the family would get the father’s salary at the beginning of the month, and strive to spend it all on food and other necessities by noon or early afternoon at the latest, before the prices went up. With luck, the haul lasted until the first of the next month, when the exercise was repeated.
     Taylor is also good on thumbnail sketches of the politicians and their motives. He emphasises the murderous mutual vilification of left and right, which came near to outright civil war. We can see the beginnings of the tangled path of cross-purposes, and more or less blatant betrayals, that led from the Weimar Republic’s inability to forge a national unity to the handing over of power to Adolf Hitler.
     The book is highly readable. Taylor has done his homework: the list of sources occupies six pages of small print. He has the knack of synthesising huge amounts of information, clarifying the narrative lines, and dropping telling details at the right places to create the personal, human scale that allows us to form an impression of reality.
     As a believable story of the times, the book is very good, As an analysis of why and how the awful events unfolded, it is weak. It’s clear enough that French intransigent refusal to renegotiate reparations payments played a key role, as did American insistence on repayment of debts. It’s also clear that the German inflation was in part deliberately induced to reduce the accounting value of the reparations. A side effect was that all that excess money created consumer demand, so for a while there was a boom. But since the money supply grew faster than production, that did not last.
     In addition, the government was unwilling to risk the effects of a limited money supply, which would have stabilised the currency, but which would also have required siphoning large amounts of cash out of the economy in order to pay reparations. The last phase, hyper-inflation, created grievous hardship.
     In short, Taylor is good at presenting the immediate causes of the inflation. He does not raise the question of underlying causes. Inflation is a puzzle: Why do people come to expect to hand over more and more cash for the same quantity of goods? And why do central banks supply that cash? Why do people believe that austerity (borne mostly by other people, of course) will generate a desired surplus of cash for payment of debts?
     The German hyperinflation is a good case study in the role of psychology in the economy. People make decisions (such as investing in war bonds) because of their beliefs about how the economy works. When those beliefs prove unreliable guides, they act on different beliefs (and spend a month’s salary in half a day to get enough food to last the month). To understand inflation we need to understand what people believe about money.
     It’s pretty clear that the dominant belief operating in the postwar period was that money is wealth. That’s why the French wanted money from the Germans. That’s why the Americans wanted the Allies to repay the money they borrowed. The French did insist that at least part of the reparations should be paid in kind (iron and coal, mostly). But what they wanted was gold marks, actual bullion, or paper money that was guaranteed to be exchangeable for gold. Neither the Americans nor the French were willing to forgive the debt owed them, nor to help Germany rebuild its economy so that they could supply the goods and services that France and Belgium needed for rebuilding. It was all about the cash. I think it not at all surprising that the German government decided to provide the cash, in the end by the wheelbarrow.
     Could inflation have been avoided? I don’t think so: devaluing currency is a handy way to reduce debt, and everybody did it to some extent (the British and Americans least of all, which is why the pound held its value against the dollar). But once people realised that cash is not wealth, and preferred things (food, clothing, furniture, jewellery, etc) over cash, hyperinflation was the predictable result. Then if inflation becomes bad enough, people are willing to swallow the bitter medicine of currency reform, and the sharp but relatively short-lived pain of adjustment to the new bookkeeping.
     Money works only as long as people trust it. Whether “backed” by gold or not, money is a measure of value, just as a meter stick is a measure of length. There’s a difference, though. The value of a dollar depends on what people believe it to be. A $10 bill is an IOU: as long as we trust it as a “medium of exchange”, it can be cashed in for real wealth: a meal, a book, a few gallons of gas, a pair of gloves, a theatre ticket, a sack of potatoes.
     Good book, worth reading as history, and as an object of meditation about the nature of money. ***

Tuesday, February 27, 2018

Read one, you want to read the next: The Oxford Book of English Detective Stories

    Patricia Craig, ed. The Oxford Book of English Detective Stories (1990) Craig has done wonderful job. A handful of the classics are here (e.g., “Silver Blaze”), and I’ve read work by many of the authors. But about half are new to me, and if the samples indicate their skill, they are underrated, for example Cyril Hare, whose “Miss Burnside’s Dilemma” shows how point of view can be used not only to narrate a crime but also to show its ripple effects.
     The collection covers about half a century, when detective stories concentrated on the puzzle, and the characters were just complicated enough to make both the crime and its discovery believable. What struck me was how little we need to be told of a character to construct an impression of the backstory that grounds motive in reality and method in plausibility. It was as often as not the style, the throw-away phrase or word, that created these impressions, I think because they create a vivid narrator. Make the story-teller sound trustworthy, and we will follow their lead.
     A potato-chip book: when you finish a story, you immediately want to read another. ***

Monday, February 19, 2018

More about the Sacketts: Ride the Dark Trai.

     Louis L’Amour. Ride the Dark Trail (1972) Some time ago, I found a stash of about a dozen books by L’Amour at the food bank’s yard sale. I sorted out te sackett series, and began reading them. This is the 2nd one.
     Logan Sackett drifts into Siwash, a town run by a greedy bully, John Flannan. Logan immediatley makes enemies when he defends a young girl. He just doesn’t like the way the men in the saloon treat her. He takes her to the MT ranch, which Emily Talon is defending against Flannan’s attempts to run her off. Flannan has killed Em’s husband, and Em shot Flannan through the knees in retaliation. So it’s as much a feud as a attempted robbery.
     Turns out Em is a Sackett, so of course Logan has to stay to help her out. Eventually Em’s sons Barnabas and Milo join them, but the final showdown is between Logan, Em, and Flannan. Along the way, Logan is shot and beaten up, but he manages to survive, because he’s one of the meaner Sacketts.
     L’Amour shifts point of view a few times, but most of the story is told by Logan. Some loose ends aren’t tied up: will Logan settle down, or will he continue to drift? Read other stories in the Sackett saga to find out! The book is a page turner, despite the occasional asides into history and geography and such. There are also odd lapses in style, with Logan now and then using decidedly bookish phrasing to describe the landscape  and weather. I’m on a L’Amour binge, so my rating is probably a bit high. The title has no obvious relation to the plot, unless "dark" is taken to mean "dim, hard to see". ***½

Sunday, February 18, 2018

Econimics 201: Thermodynamics and efficiency

Thermodynamics and economics: Why a car is the most expensive mode of transport.

A typical gasoline engine in a car runs at about 25% efficiency. That is, the energy in 1 out of every 4 litres (or gallons) of fuel in the tank does “useful work”. The energy in the other three litres is used to run the engine and transmission, to push exhaust out the tailpipe, or is converted to waste heat. (Efficiency in the lab can be much higher, but we’re talking real-world here, not lab conditions).

The “useful work” consists of moving the car. So about 1 of 4 litres of fuel is used to move the car and its driver. Let’s assume the car plus driver weighs a tonne (1000kg), of which the driver weighs 90kg. Since a litre is 1,000ml, the system burns 1ml of fuel per kg of weight. Of this, 90ml will be used to move the driver. The rest (910ml) is used to move the car. So out of a total of  4,000ml of fuel, 90 ml is used to move the driver. That’s approximately 1/4%.

Therefore: 1 the fuel costs $1/litre, you’ve spent $4 to move yourself, of which 1 cents’s worth of fuel moves you, 96 cents’ worth moves the car, and $3 pays for rotating the engine, pushing the exhaust out of the tailpipe, and waste heat. One can scavenge some of that waste heat to warm the cabin in winter, so it’s not entirely wasted.

The above calculation ignores the effect of speed, because speed increases fuel consumption overall. However, since an increasing fraction of the energy is used to push air out of the way, the fraction used to move the driver decreases. In other words, at most 1/4% of the fuel moves the driver down the highway.

I’ve also ignored the effect of passengers, stuff in the trunk, etc, since those merely increase total weight and hence total fuel consumption. The amount of available useful work will still be about 25% of the energy in the fuel. The fractions for moving the car and moving the people in it will change somewhat: in general, a loaded car will transport people and their gear more efficiently than a nearly empty one.

But however you tweak the scenario, using a car to transport people is appallingly wasteful.