Last time we looked at combustion, now we'll see how we mix up the fuel.

The float carburetor became popular around the turn of the century (not this one, I mean 100 years ago), and was used in cars up till fuel injection took over in the mid 1980's. Most worked by constricting the incoming air through a Venturi. The air, going through a constricted passage had to travel faster, causing the pressure of the air to lower. A fuel nozzle in this area sucked fuel through a jet (small hole) from the float chamber.

The float chamber was just a miniaturized version of a toilet tank, its function was to hold fuel at a specific level so the suction from the fuel nozzle drew in the correct amount. A fairly cheap and simple system, really.

What could go wrong? A number of things, actually. The most common was dirt holding the float valve open so the gas level would get too high, and excess fuel spills out the nozzle, flooding the engine. Another was dirt plugging the jet, so too little fuel flows and the engine starves. The good news was that it was mostly field-repairable. Going around a corner too fast caused the fuel level in the bowl to fluctuate. Another problem
with carburetion is the inability to detect the density of the air. Thin or hot air goes through with the same velocity as cold or dense air, but doesn't carry the same amount of oxygen, so the mixture was not accurate.
Remember the black smoke of cars running overly rich in the mountains? Thin air caused this. 
The intake manifold connects the carburetor to the cylinder head. Because the air and fuel mix in the carburetor, the intake manifold has to be heated to keep the fuel from condensing out on the surfaces of the passages. If it does, some parts of the mixture are too rich and some too lean. A choke is needed when cold to cause the carburetor to suck more on the fuel nozzle in an attempt to get most of the mixture rich enough to fire. The choke is a flap on the air cleaner side of the carburetor. In later years, they were automated. 

Fuel injection gets around many of these inaccuracies. Air quantity and quality can be measured with mechanical flaps or electronic devices. A mechanical or electronic computer directs fuel to be sprayed from a nozzle right at the intake valve where it doesn't have much time to condense, so heating the intake manifold isn't required. Keeping the air cold leaves it denser, getting more into the engine, so more power and economy result. By spraying at high pressure, the fuel is atomized finer, so it burns more easily, completely, and cleanly.

These are the reasons that virtually all cars today are
fuel-injected. 

Superb motoring,

John M. Elliott

For an internal combustion engine to function, something is needed to get the combustion started. One of the first methods was the hot tube. A thin tube was connected to the cylinder head, it stuck outwards several inches, and had a kerosene lamp flame under the closed end. Compressed mixture gets forced from the cylinder outward in the tube, ignites when it gets to the hot portion, and fires back into the combustion chamber, igniting the rest of the mixture. The first Daimlers worked this way. Timing could be adjusted by how hot the tube was kept. These engines operated at very low speed.

Another early scheme was called “make and break”. This was a set of contacts located inside the cylinder head area, operated through a rod which was turned from the outside. It was hooked up in series with a battery and induction coil. When the contacts opened, a spark was formed and ignited the mixture. This set-up was used a long time in marine application because it ran at low voltages and was not effected by water. It was somewhat hard to service, and the contacts were prone to getting dirty and wearing.

The real revelation in ignition was called jump-spark, and is still the standard today. Only a fixed set of electrodes is inside the cylinder. This is the spark plug. It is merely an electrode surrounded by a ceramic insulator (originally mica) and a threaded case. A gap is formed between the electrode and the grounded case. High voltage applied to the center electrode jumps the gap, and arcs to the case, this spark igniting the mixture.

To get the high voltage, power from a battery flows through a set of contacts (points) to copper windings around an iron core. The magnetic field saturates the iron core. When the points open, the magnetic field collapses causing high voltage to form in another winding surrounding the iron. These windings are connected to the spark plug, and cause the plug to spark. By using a few turns of heavy copper wire for the battery side, and many many turns of fine copper wire for the plug side, the ignitiion coil has the ability to step up the battery voltage thousands of times.

It’s so simple, what could go wrong? Well, first off, the plug still lives in a nasty environment. If deposits build up on the insulator, it may stop insulating. This is called “fouling”. Deposits may also glow from the heat of combustion and cause pre-ignition when the ignite the fuel before the spark comes. Better fuels without lead additives have greatly extended plug life by limiting deposits. The electrodes wear so the gap increases, and the surfaces round off making it more difficult for a spark to get started. Great care is taken designing plugs so that the center electrode gets hot enough to burn off fuel and oil deposits, heats the surrounding mixture to near ignition temperature, but does not get too hot and pre-ignite fuels, or melt itself. Many cars today can go 100,000 miles before needing the plugs changed, but I wouldn’t want to be the guy trying to get them loose.

Ignition coils could last forever, and for practical purposes most do. Vibration may break internal wires, or the insulators may deteriorate, but that’s about all. Points have been replaced by computer controlled electronics, and so has the distributor - a device which mechanically determined spark advance and sent the spark to the proper plug. While only one coil was needed with distributor ignition, it was complicated, bulky and expensive. Today’s computer does a better job of timing ignition, and one coil for each plug or two is cheaper and more reliable than a distributor. Some makes have even put the ignition coil around the plug, eliminating the high voltage wiring. Most problems with ignition today are related to sensors, rather than the components that make the spark.

Care of spark plugs: They’re so cheap, best throw them out at the change interval. For those wanting to clean, things have gotten harder since the 20’s. Up until that time, sparkplugs were disassembleable. Blasting clean with walnut chips is good, and doesn’t leave grit like sand would to get into the engine. Don’t use a wire brush, as the wire will leave conductive streaks of steel on the insulator. Electrodes should be filed so that the corners are sharp, like they are when new, and gapped to spec.. This makes it take less voltage to get the spark started. Platinum and other rare metal plugs have delicate center electrodes which can be damaged by the slightest touch. Always recoat threads with anti-seize compound before installation.


Superb motoring,

John M. Elliott

There has been some talk in the news about the Honda Accord with 1,080,000 miles, and the Volvo with over 2,000,000. Of course, the owners are blowing enthusiastically about their respective cars. It kind of reminds me of the farmer bragging about the axe he inherited from his grandfather......while he replaced the handle 5 times and the head twice, but it's still the same great axe.

So, one of the first things is a persistent owner. It always helps if there is good quality of materials and design. I'm still driving a 1912 Maxwell (fore runner of the Daimler-Chrysler Corporation), and while it may be 90 years old, I expect it will still be going years from now while most cars bought new today will be in the dump.

Great strides were made in engine durability as a result of emission control. It isn't just that the engines had to last through the emission warranty. Adding positive crankcase ventilation did away with the draft tube, and thus sealed the crankcase to external dirt entry. More precision fuel mixtures make for cleaner burning and less oil pollution. Fuel injection got rid of chokes, which had a bad habit of washing the cylinders with gas and compromising lubrication. Oils themselves have been improved in lubricity, corrosion resistance, and ability to handle contaminants. 

It would be easy to cite better materials and machining practices (tolerances), but it's amazing how good materials and machining was 100 years ago. It's just gotten easier to adapt them to mass production, and emission controls demands it now.

Better road conditions are another factor. Most of us don't have much call to drive on gravel roads these days. Lots of them still exist, but for the most part, we get around with out all the dust and grit from poor roads getting into the workings of the cars.

If a person wanted their car to last, there are a few simple things that would make the job easier. Wash the car regularly, especially after salty roads. Do regular maintenance, the owner's manual is a good guide, and not many cars have been harmed by too many oil changes, etc. Go easy on the throttle until the car is warmed up; it usually takes about 1/2 hr. after the coolant temperature is up for the oil the get warm. Don't leave the car idling needlessly. Don't let others drive your car out of your presence. And if you really care, keep up on repairs. There really isn't any limit on how far or long an auto can go. With some makes, it just a bit easier.

Superb motoring,

John M. Elliott

Combustion, for this discussion, is limited to a fuel flaming in air. This is an exothermic reaction (heat is released) For a fire to occur, three things must be present: fuel, oxidizer (air), and an ignition source. Fires are put out by elimination of one or more of these factors. Only gasses burn, solids and liquids don't. What actually burns is their vapors. Yes, solid wood doesn't burn, liquid gasoline doesn't burn. Before a solid or liquid can support combustion it must be raised to at least it's flash point. This is the temperature at which a spark over the test item will cause a pop as the vapor ignites. The flash point for gasoline is ~ -45F, diesel is ~ 126F, that of wood is ~ 450F. Raising the test item a few degrees more brings it to it's flame point, where the vapor will stay lit without the spark. The ignition temperature is that temperature at which a very small sample of the test item, when injected into a heated atmosphere, ignites. The ignition temperature of gasoline is ~ 536F, that of diesel ~380F, that of wood ~ 450F - interesting because when wood is raised to it's flame point it spontaneously ignites. Also note that flash point of diesel is far higher the gasoline, but the ignition temperature lower. 

The heat of combustion is dissipated by conduction, convection, and radiation. If you have tried to light wood fires, you might have noticed that it is easier to get two or more pieces of wood to burn that one. This is because each will radiate it's heat to the other to help keep the wood above the ignition temperature. Wood near a cold steel plate is hard to burn. This is because conduction and radiation lower the temperature. It is hard to light a big log with a match because of conduction of the match heat to the rest of the wood. Cutting the wood into shavings eliminates this problem by increasing surface area and decreasing conduction. Another factor of combustion is mixture. If the there is just the right combination of fuel and oxidizer, the flame will be it's hottest. If there isn't enough fuel, heat will be wasted raising the temperature of the air not used in the combustion, and eventually it will fall below the ignition temperature. Too much fuel will have a similar effect, heat will be wasted because the fuel
doesn't have enough oxygen to decompose completely. Carbon monoxide results rather that dioxide. When there is way too much fuel it can hardly vaporize, the heat needed for vaporization robs the mixure of its ignition temperature, and the engine is said to be flooded. 

And so it goes with combustion in a car engine. If the gasoline is vaporized by fuel injection, smaller droplets are formed and are easier to heat to a vapor, ignite, and burn more completely. Flame near the cylinder side or head are cooled and don't burn completely. This is why modern engines try to minimize surface areas of the combustion chamber. The flame
is quenched in the narrow areas between the piston and cylinder, so the ring is moved up to make the space smaller and pollution less. The speed of combustion is dependent upon fuel (grade) and the temperature (related to compression ratio because the mixture is heated considerably through compression). If the flame travel speed get into the supersonic range, the
combustion is said to detonate. When the shock wave hits the cylinder side or head, the sound will be heard outside the engine as a knock.

There you have it, what could be simpler, a little fuel, a little air, a squeeze, a spark, and bang---power.

Superb motoring,

John M. Elliott

Usually, when having engine problems, a knowledgeable person can make a good guess as to what is wrong based upon probability theory.
This is what familiarity with the make can do for you. Dealers and others that work mostly on the same models know the history of problems. To fix a given problem, first replace part "A", and if that doesn't work, then try part "B", then "C" and etc. While it might not sound too good, it is an effective approach, and certainly sells parts. It can even be effective with unskilled workers if they have access to the sheets that tell the likelihood of problems
with specific parts. Many times cars are built with design defects, and Technical Service Bulletins, issued by the car maker, explain the problem and solution. Mechanics commonly called these TSBs "poop sheets".

Now and then, a problem comes up that hasn't happened before (actually all problems had a first time). This is when one must go back to basics. For an engine to run, it must have: air and fuel properly mixed, compression, ignition, and exhaust. If any of these are not optimum, degradation of running ability occurs. Ignition is usually the first thing one looks at, because it is easiest, not most likely. Next is mixture because it is most likely. It can be affected by many things such as fuel quality, atomization, vacuum leaks, improper injection pressure, miscalibration of the controller, just to name a few.
The point is if one understands the basics, they can then go on to isolate the factors that might affect each of the four basic components to internal combustion. A little thought can go a long ways towards finding a solution, rather then just randomly replacing part. Back up and start with the basics.

Superb motoring,

John M. Elliott

No sooner than cars began to go, they needed to stop. This is done by converting the kinetic energy of the motion of the car to heat. The amount of heat is determined by the weight of the car and its speed. It took an Einstein to figure it out but the energy goes up the square of the speed (E=MC^2). This means that a car going 60 has to dissipate 4 times the energy as one going only 30. The higher the performance of the car, the better brakes that are needed. There has been a lot of development in brakes over the years, and today we have mostly drum or disk variety - Stepping on the pedal moves a lever with a mechanical advantage of about 4 to one to a booster which uses vacuum or hydraulic from the power steering pump to augment the forces, and then presses a hydraulic plunger which sends brake fluid under high pressure to the wheel cylinders. 

For the drum there are a couple of curved shoes which are connected together at one end, and a hydraulic cylinder on the other end. The piston in the cylinder forces one shoe against the drum which rotates it towards the other, which then moves tighter to the drum. This gives a self energizing effect which means less mechanical advantage is needed to function. The downside is any inconsistency in friction gets amplified. And drums can't easily rid themselves of contaminants.

Disks are simpler, lighter, wipe themselves clean, have no self-energizing effects, and are easier to service. Hydraulic pistons in calipers push pads against a disk. Greater forces are involved in the clamping action, so usually some form of boost is required to keep pedal ef-
fort low. Often the emergency brake requires separate parts, like a miniature drum inside the disk. 

While the concept of brakes is simple, the devil is in the details. The drum or disk must withstand high temperatures, retain its shape and friction level, resist corrosion, wear, and be cheap to manufacture. The pads or shoes need to have consistent performance at temperature
extremes, be non-toxic, long lasting, low dusting, and inexpensive. Unless you're racing with a near limitless budget, there are going to be some tradeoffs between the various factors- Generally speaking, the more expensive cars end up with the better brakes because more is spent in engineering and materials. Related do-dads can add anti-lock, traction control, or skid control.

Superb motoring,

John M. Elliott

One would hope we've seen the end of the snow and salt by the time you read thins. I usually figure approximately April 15 as the end of winter, and time to change to summer tires. It may still snow or be icy, but it won't amount to much. When we think the real end has come, it's a good time to wash of the vestiges of winter. The easy way to start is with a commercial car wash that does the underbody wash. This should leave the car clean enough to begin the hand work. With a garden hose, rinse out the fenders, paying particular attention to the lips where sand accumulates, suspension pieces such as spring seats, and up above the gas filler hose (many of these are in the rear fender) . The bottom edge of the door, if it has a rubber seat gets sand, salt, and dirt trapped on the lips and ledges. Lift the hood and rinse out the engine compartment. Sometimes this is a good way the rinse the salt out of the fender liners. Rinse the hood itself too. If by chance all this rinsing gets the ignition wet so the car won't start or misfires, it means these components are not up to standard (British cars excepted), and this should be looked into.

Check the air intake at the base of the windshield for leaves and debris. On newer cars, the wiper arms have a parking place, which also catches debris. Look at the fuel filler door area too. Hatchbacks can collect dirt in the channel at the top of the hotel

There are usually drain holes in the bottom of the doors, rocker panels, quarter panels, and various underbody structures. These holes can get blocked with dirt and this is the major cause of rust outs. Clean these holes out with a Popsicle stick or similar non-scratching tool. While in the area, it may be a convenient time to clean the door jams.

After the rinsing, take a drive to dry things out. This is the easy and fun part. A half-hour drive usually does the job, but for the dedicated, 3 hours is about right. One final step might be to spray a preservative oil or wax on the underbody and into the closed panels. There are many products on the market, and also some risks in there use. Asphalt based products have only cosmetic attributes, tend to harden into layers which separate from the body, and allow water to get behind. This is a negative for rust prevention Waxy oils such as LPS-3 help prevent rust but collect dust (makes dark smudges) and the odor might be disagreeable. Amzoil has just come out with one, but I have yet to try it, Be very careful with any product not to get it where it doesn't belong, such as the window guides in the doors. You don't want to gum up the window mechanism.

Superb motoring,

John M. Elliott

New on the horizon are higher voltage electrical systems for the high-end cars. BMW and Mercedes-Benz are working on 42 volt systems due to come out in a couple of years. Actually, like most things automotive, the idea isn't really so new; many electric cars had 48 or 60 volt systems 85 years ago or more. It was for the same reason as today; the need to move power with smaller wires.

The 42 volt nomenclature is somewhat confusing. Lead-acid batteries produce about 2.1 volts per cell under moderate load. A six volt battery was called that because it produced 6.3 volts. A 12 volt battery was then called 12 because it had twice as many cells as a six volts, but it actually puts out 12.6 volts. When a car is running, the alternator or generator has to be a few volts higher to charge the battery. A 12-volt car is really running at about 14. The car that runs at 42 volts has what would be called a 36 volt battery. Incidentally, this was the common system for wind power systems popular on farms before rural electrification.

A little about electricity. Power (watts) is the product of volts times amps. Voltage is analogous to pressure in water, amps to volume of water. The more pressure (voltage) and the bigger the hose (amps) the more water (power) can come through it. The size of the wire determines how many amps can flow through it. Insulation is required to contain the voltage, although thickness sufficient to protect against abrasions and cutting is enough to handle several hundred volts.

The end result is that by going to a 42 volt system, the same wire that was in a 14 volt system can carry 3 times the load or the same load with 1/3 the losses. With so many electrical things being operated in cars now, the weight of the wire and the size of the cables is becoming a factor in lightweight designs.

It's somewhat surprising that they didn't go to a 24 volt system, as they are in common use in airplanes, trucks and buses. That would make many of the components such as small motors and light bulbs readily available at reasonable cost (although the airplane people would argue that).

Superb motoring,

John M. Elliott

Simply put, a relay is a remote controlled switch. A small electromagnet is used to move large or multiple contacts so that something that needs lots of power can be controlled by a small switch. A very common use is in the starter circuit. The starter motor needs several hundred amps of current to start the car. That is why the battery cables are so large. A relay makes it so that heavy wire doesn't have to be run up to the key switch, and the pans of the key switch can be small.

Another function of some relays is to control multiple devices which need to be electrically separated from each other. This is done by having multiple sets of contacts inside the relay. Relays come in many sizes and configurations. Relays can perform logic functions too. This is because energizing the electromagnet can be made to open a connection as well as close one. Complex controls can be built using a few relays. With a simple timing circuit, a relay becomes a turn-signal flasher. Headlights, heater/AC blowers, and radiator fans are typically controlled by relays. Even simple cars today may have 10 or more relay.

What can go wrong with a relay? Mostly the contacts inside may fail from arcing, corrosion, or mechanical fatigue, or the connections to the relay fail through corrosion. Most relays are mounted in sockets, so they are as easy to change as a light bulb. The mechanic makes his money by knowing which relay is giving trouble, and where it lives.

Superb motoring,

John M. Elliott

Technology from aircraft and racing cars is starting to trickle down to production cars. Carbon brake disks made by trending carbon fibers with chemically cracked carbon molecules have twice the heat absorption capacity, a 50 percent higher coefficient of friction, and one-fourth the density of iron. Ceramic pads should last twice as long as conventional pads. Better braking isn't the only benefit of carbon disks, however. They save 10 pounds of unsprung weight at each wheel, which has a major impact on rough surface handling. It may be a while before this nifty $7,500 (!) option trickles down to my class of cars. Actually, it seems the world may be going mostly the other direction. The Ford Focus cars I saw in Europe all had four-wheel disk brakes, but the ones I have seen here have drums on the rear. The research and development has been done, the tooling made, and yet
they feel the need to revert to cheap old tech. Maybe drivers here are more interested in cup-holder development?

The Firestone debacle has brought up some interesting points about tire pressure. The Wilderness AT tire is supposed to have 35 psi at its rated load. Since there isn't nearly that much load on them, it's not surprising that Ford recommended lower pressures for better ride and less traction to prevent rollover. However, at 26 psi, it may be that too much of the safety margin has been given away. Suppose you check the pressure after driving a mile or so, instead of cold? Or you gauge reads a couple of pounds high? And then tires usually leak down after awhile. When some of these things combine, it wouldn't be hard to Find this 35 pound tire down close to 20 pounds, and that is going cook the tire at highway speed until ... POW! 

The lesson, then is if you use inflations much below the rated pressure, great care must be taken to ensure that accurate readings and careful maintenance guard against further drops.

High speed driving or heavy loads may require raising the pressures to safer levels.

Superb motoring,

John M. Elliott