Magnetic Gears Reduce Friction

Friction between moving parts in the engine and transmission consumes a considerable percentage of all fuel used by a vehicle. Any technique for reducing this friction gives an increase in fuel economy. Here is a demonstration of two magnetic gears which use magnetic fields to transfer force instead of gear pins in physical contact. Avoiding metal on metal contact leads to much, much less friction in the system. Of course, generating magnetic fields strong enough to support the loads experienced by transmissions in contact with a couple of hundred horsepower engine is more than challenging. But it is always good to keep an eye out for possible future technologies that could help us save on gas.

Roil Platinum for Better Lubrication

Friction between moving parts in engines burns fuel. Generally less friction means you will save on gas. So better lubricants could improve your gas mileage. Roil Platinum is an oil additive which seems to do a pretty good job on fighting friction based on the video below. You might want to try it out and see what happens. You will have to do careful measurements of fuel consumption before and after to be sure. The best is to have a real time fuel consumption gauge, such as the ScanGauge.

Ships Reducing Drag to Save on Gas

Ocean going cargo vessels are responsible for moving an important part of the global economy. Consider how much of the items you buy in the US are made overseas and have to be brought to you by ship. Moving a huge ship against the resistance of the water costs a lot of gas. Ships are enormous gas guzzlers. Ideas for saving on gas in shipping could be very important for us in the future given our massive dependence on seaborn imports.

Synthetic Oil Could Help Your Truck Use Less Gallons Per Hundred Miles

If you have a big, gas hungry truck what can you do to save on gas? Well, one option could be the use of low friction synthetic oils. This video shows a dyno test run with a synthetic oil called Royal Purple. The dyno showed that immediately after replacing the oil with the Royal Purple synthetic the drive train friction was reduced. You might want to try it out too. One thing to keep in mind is that if you are replacing old oil, you could see an improvement without a synthetic. Oil oil is probably going to result in more friction than new oil. So on the dyno, you would really want to empty the old oil, replace it with new oil and then run the numbers. Then replace the oil with the synthetic and see what numbers the dyno posts up. Then you can compare fresh oil to fresh synthetic. The use of a dyno makes this result valuable. Only a dyno can give you a clear number.

Regenerative Braking

Motion requires energy. To overcome inertia and add speed to a body, energy must be added. The energy a body has by virtue of its motion is called kinetic energy. The formula giving the amount of kinetic energy K that a body of mass m will have at a speed v is K = ½mv². Note the occurrence of the square of the speed. That means doubling the speed does not double the energy needed but rather quadruples it. Now energy cannot be created or destroyed. So to get your car up to speed the required kinetic energy has to come from somewhere. In a standard internal combustion engine driven vehicle, this energy comes from the chemical energy that was stored in the fuel, in the gasoline or diesel.

When you want to slow down or stop the kinetic energy will be lower at the new lower speed. Since it cannot just be destroyed, this energy must go somewhere. In a normal vehicle it is converted to frictional heat in the brakes. This heat then escapes and the energy is lost forever. Every time you slow down, you are throwing away all of the chemical energy that came from the fuel. Your brakes slow you down and in the process turn gasoline into heat.

What if it were possible capture the kinetic energy that is lost as you slow down and store it for reuse later? Obviously it cannot be converted back into chemical energy in the fuel. Internal combustion engines and standard brakes have no way of capturing the kinetic energy and it must be lost as heat. This is the reason that the Golden Rule of Hypermiling is "Maintain Momentum". Every time you slow down and speed up again, you have turned some fuel into heat.

Electric engines, such as used in hybrid vehicles or NEVs can capture some energy while slowing down. This is because electric engines run off of batteries, which can both provide and store electric energy. Compare that to liquid fuel, which can put energy out but it is impossible to pump energy into. Also an electric engine run in reverse is in fact an electric generator. Depending on which direction you run it, an electric engine can draw stored energy out of a battery to provide work or it can accept outside work, generate electricity and store it in the battery. Regenerative braking basically switches the electric engine to run in reverse, in generator mode. It makes the spinning wheels and drivetrain do work on it. As the drivetrain torques against the electric engine, it slows down, thus slowing your vehicle down. The drivetrain torquing the engine allows it to generate electricity, which is then stored in the battery.

Although regenerative braking is not capable of capturing all of the kinetic energy due to inevitable losses, any percentage it does recover is available to accelerate you back up to speed without needing to put in fresh energy. Unlike normal internal combustion engines and standard braking systems, not all of your motion energy is lost when you slow. And that means you save on energy.

Where Does the Energy in Your Tank Go?

Energy cannot be created or destroyed, only converted among its various possible forms. This physical fact is known as the First Law of Thermodynamics. So what happens to all of the energy in a tank of gas? How much of it performs useful work and how much of it is wasted? Where are the losses? Of course for a vehicle, the useful end purpose is to move passengers and cargo. Anything else is waste. This excellent paper has a nice breakdown of where the energy goes. It considers a composite driving cycle including both highway and city driving. The results go as follows.

We start with 100% of the energy in the fuel, and the table shows where it goes.

Fuel Energy Destination

Destination	Percent
Irreversible Combustion	30
Cooling and Exhaust	32
Engine Friction	18
Accessories	2
Transmission	3
Air Resistance	5
Tire Rolling Resistance	5
Brakes	5

Irreversible combustion refers to the fact that during combustion, a portion of the energy is necessarily converted to forms not available to do work. That is a basic result of thermodynamics. No heat engine can escape this. A heat engine is one that generates work by using energy to heat a working fluid, and then allowing this hot working fluid to expand. The pressure generated during the expansion then does the work. By directly converting energy to work, for example in a fuel cell or electric engine it is possible to avoid this loss. However, automobiles are still overwhelmingly using the internal combustion engine. Car engines are definitely heat engines. They use the energy in the gasoline to generate heat by burning it with air as oxidizer. Then the air is heated up. The same hot air + combustion products serves as the working fluid.

The 30% lost to the cooling system and the exhaust is partly recoverable. Saving some of this energy is the basis for turbo compounding engines and six stroke engines.

Engine friction refers to losses in the moving parts of the engine itself. There are engine designs, like the Brickley engine that focus on reducing these losses. In particular, modern high precision machining techniques are allowing cheap production of complicated friction reducing designs. Machining tolerances have decreased as well, also allowing for new lower friction designs.

The numbers are representative of a typical vehicle averaged over a typical driving cycle. Under specific conditions, say going 60 MPH up a 3% grade, the values will break down slightly differently. Only 20% of the energy in your gas makes it out of the engine. That 20% is where you have control. You can't do much about thermodynamics or engine friction. But the 2% typically diverted to accessories represents 10% of the out of the engine energy. Reducing use of the air conditioner is an example of exerting control. The 5% of the total typically going to air resistance represents 25% of the past the engine energy and you can control that by reducing your speed.

The table shows that it is the engine designers of Detroit that will have to bear the largest part of the load on the way to better fuel economy. And if they won't do it, then there are plenty of smart engineers in the rest of the world who will do it and are doing it.

Resistance to Motion

Your car has to fight against friction to maintain its motion. There are two categories of friction: internal friction in the engine, the transmission and every other component where moving parts are found and external friction. Here is a breakdown of engine friction by subsystem. The external friction comes from rolling resistance in the tires and air drag.

The resistance of the tires depends primarily on the contact area with the road. Minimizing this area minimizes friction. In the picture you can see than underinflated tires have flat, square contact areas. The outer edges of the tires touch the road. Correctly inflated tires will not touch the road with the outer edges. Overinflated tires will have even less contact area and less friction but they will give you a bad, bumpy ride. It is even possible to damage the undercarriage of your vehicle with overinflated tires because they will not be helping to soak up shock and vibration.

The air resistance depends on the shape of your vehicle and the speed you are going. At low speeds the air resistance is low and increases slowly. At higher speeds the air resistance is large and increases rapidly. Low speed driving is dominated by tire resistance and high speed driving by air resistance. The tire resistance is constant, basically independent of speed. The chart above compares the tire and air resistance and shows their total.

Knowing the relative contributions of tires and aerodynamics helps understand what is happening. For example, there is a debate about whether running the air conditioner or opening the windows (and thus increasing air drag) is better for gas mileage. Since the open windows add to air resistance which is small at low speeds, we can tell that for low speeds windows down and air conditioner off saves on gas.

Conventional Continuously Variable Transmissions

A few posts ago we talked about the NuVinci continuously variable transmission during our series on gas mileage technologies. The NuVinci design is an innovative type of continuously variable transmission that has not yet been used by a major automaker. However, there are other types of conventional continuously variable transmissions that have been used in cars. These are conventional in comparison with the NuVinci, but advanced compared to the common manual or automatic transmissions in almost all of our cars.

Everyday transmissions adjust the ratio between the rotational speed or RPM of the engine and the wheels by choosing from four or five fixed metal gears. Current continuously variable transmissions use a pair of variable diameter pulleys instead of the gears. Each pulley is formed out of two cones with their tips or apexes pointing towards each other. These cones can move closer together or farther apart. A hydraulic or spring system is used to control the spacing between the cones.

A belt runs between the pulleys, fitting in the groove between the two cones. Older designs used rubber belts that were shaped like a V to better contact the sides of the cones. Now with newer metal alloys there are metal belts. The metal belts are stronger and allow for transmissions that can support much higher torques. The idea is that as the cones move farther apart, the belt can slip farther down between them and get closer to the pulley axis. The lower down the groove the belt is the smaller the effective diameter of the pulley.

It is necessary to have variable diameter pulleys in pairs. If one pulley pushed the cones closer together forcing the belt up the groove and increasing the belt diameter the belt would have to stretch if the other pulley did not simultaneously decrease its diameter the same amount. One pulley of the pair is connected to the engine crankshaft and the other to the vehicle driveshaft. As they change their diameters in lockstep the ratio of crankshaft diameter to driveshaft diameter can vary continuously. The ratio of these diameters is in inverse proportion to the ratio of their rotational speeds or RPM. If for example the largest diameter (when the cones are close together) is double the smallest diameter (when the cones are far apart) then the output (driveshaft) RPM can vary continuously between one half the input (crankshaft) RPM and double the input RPM.

The result is better gas mileage due to two main factors. One is the fact that the engine can run closer to its most efficient RPM more of the time. The second is that the transmission is very simple so the losses due to friction within the mechanisms are reduced. These factors give a 6% increase in fuel economy.

What Does Engine Oil Do?

The picture shows that sometimes we need friction so we don't go sliding out of control. One place where we do not want friction is in our engines. Engine oil is there to lubricate the metal surfaces and get rid of friction. In a properly working engine, a thin layer of oil separates all metal parts so that there is no metal-metal contact. Instead we find metal-oil-metal contacts. But reduce friction is not all that oil does.

Oil also helps to cool the engine. There are places where the water cooling system just can't reach, like down in the crankcase. Oil gets in these areas and removes the heat. Another role of oil is to help the piston ring seal the combustion chamber or head off from the crankcase. Oil also scavenges tiny metal particles which are worn off when engine surfaces work against each other. These particles are then removed from the oil by the oil filter. Acids can be formed by chemical processes occurring in the combustion of fuel. All gasoline has at least a small amount of sulfur in it. This sulfur can react with water (brought in with the air) to produce sulfuric acid. The sulfuric acid is dissolved in the oil, which has acid neutralizers in it.

Brickley Engine - Less Friction, Better Mileage

Friction in the engine itself lowers your car's gas mileage. Instead of begin converted to useful work, some of the energy in the fuel is wasted in the form of heat or noise. Mainly heat. The Brickley engine design aims to rearrange the cylinders and crankshaft arms to reduce this friction. A Brickley engine is an internal combustion engine with specially connected pistons that move along paths to a very high tolerance. Because the piston stroke is defined to a couple thousands of an inch, the piston skirts can be eliminated or reduced. So far this engine exists only as a patent. I doubt there are working models. Not to say I doubt they will work, just that there is still no prototype. Apparently the Brickley design can eliminate 35% of the engine friction. This could give a 15% to 20% increase in vehicle mileage.

One other interesting bit of information was a list of components and their contribution to friction in a typical engine. Here is the breakdown of engine friction by part according to Mike Brickley, the engine designer:

Research attributes the following approximate amounts to the various components: crankshaft 18%, connecting rods 15%, accessories 10%, camshaft 15%, piston rings 21%, piston skirts 21%.

Engine Friction Breakdown

Component	Friction
Piston Rings	21%
Piston Skirts	21%
Crankshaft	18%
Camshaft	15%
Connecting Rods	15%
Accessories	10%