Suck, squeeze, bang and blow

Human's love affair with the four-stroke engine

There are millions of cars on the road today, and the number of motor vehicles is sharply increasing regardless of the price of oil and expensive maintenance costs. But many people still don't know how these motor vehicles actually work or realize the full effect they have on the environment?

Your auto's Otto cycle

This picture shows a single cylinder of a four stroke engine.

Most motor vehicle engines operate by using the principles of the Otto cycle, which was patented by the German engineer Nikolaus August Otto in 1876. It was learned that a Frenchman named Alphonse Beau de Rochas had actually conceptualized this process earlier, so Otto lost his patent even though the process still bears his name.

The Otto cycle is used to move a piston up and down inside a metal cylinder. By connecting pistons to a crankshaft, the up and down movements are turned in rotation. This rotation is transferred to the wheels of the car via the gearbox, which enables the car to be driven at a wide range of speeds. The Otto cycle has four strokes, which are known as "suck, squeeze, bang and blow."

The "suck" stroke is when a mixture of fuel and air enters the cylinder through the intake valve as the piston moves down the cylinder. Its proper name is the induction or intake stroke.

The next stroke is called "squeeze" or compression stroke. Here the piston moves up the cylinder with both valves closed. This increases the pressure on the fuel and air mixture.

The third stroke is the "bang" or ignition stroke. The compressed mixture of fuel and air is made to ignite by a tiny spark from a spark plug. The explosion pushes the piston back down the cylinder. This stroke is sometimes called the power stroke.

Last of all is the "blow" or exhaust stroke. This is when the exhaust valve opens and the piston moves back up the cylinder pushing out the waste gases. The cycle then begins again and repeats, as shown in the table.

The most common type of engine has four cylinders with all pistons connected to the same crankshaft. The cylinders have their power strokes in sequence, so the crankshaft keeps turning. Click on the following link to see an animation of a four stroke engine in action: http://en.wikipedia.org/wiki/four-stroke_cycle

Diesel is different

The diesel engine also has a four-stroke cycle. However, during the induction stroke only air is taken into the cylinder at first. The air gets compressed more in a diesel engine than in a gasoline engine. This makes it very hot. When the fuel is finally injected at the end of the compression stroke, it explodes without needing a spark from a spark plug. The cylinder is pushed down as before providing the power to turn the crankshaft. The exhaust stroke then follows.

Both diesel and gasoline engines are called internal combustion engines because the fuel is burnt inside the engine itself. Earlier engines, such as steam engines, burnt the fuel separately in a boiler then sent hot steam to the engine for energy.

Diesel engines are bigger, heavier and noisier than gasoline engines; however, diesel engines are much more efficient. This means that they convert more of the fuel's energy into movement. A modern diesel engine can be 45% efficient, while a gasoline engine is only about 30% efficient. Still, these figures point out that the majority of energy is wasted. Energy is lost mostly in the form of heat.

Unfortunately, diesel engines produce something dangerous to our health - tiny carcinogenic (cancer-causing) particulates that make respiratory problems such as asthma or bronchitis much worse.

Environmental issues

More than 80 million barrels of oil are used up every day, and this energy resource can't be replaced. There is also the problem of disposing used engine oil, which is highly carcinogenic. With environmental issues in mind, car manufacturers are searching for ways to improve energy efficiency and make auto-related products recyclable.

Energy efficiency has been improved by making cars more aerodynamic, which reduces air resistance that slows down vehicles. Motor vehicles can be made lighter by using aluminum instead of steel, reducing the amount of energy needed to move them. Modern engines have built-in computers that constantly monitor temperature, exhaust and performance, making millions of calculations each second to keep the engine running as efficiently as possible.

Everybody can help by making energy-conserving changes. Public transportation can be taken more often, and people can avoid using cars for short journeys. We can drive more slowly on the open road and avoid leaving the car engine idling. The air conditioning in a motor vehicle can be lowered as well.

A doomed affair?

Our obsession with motor vehicles has lasted more than a century and shows no sign of abating. Motoring has become a leisure activity as much as a necessity. Many people own motor vehicles solely for pleasure and are obsessed with driving faster and faster.

The manufacturing and financing of motor vehicles have been altered as well. Ford Motor was the first company to mass-produce cars on an assembly line. This meant they could produce more cars at a faster rate. Ford offered customers loans so that autos could be purchased on down payment and paid back later with interest. In result, the Ford Model T is one of the most successful cars ever built and over 15 million were produced from American production lines between 1908 and 1926.

It doesn't look like we will be able to give up the automobile any time soon, but at some stage a radically different technology will need to replace our oil dependence. A few recent scientific developments are worth mentioning.

The Nevis (New exhaust valve and intake system) claims to double the fuel efficiency of internal combustion engines by using a new technique known as the Bortone cycle.

Also, hydrogen fuel cell technology produces electricity that can power cars. The PAC II team from Switzerland recently got into the Guinness Book of Records for fuel efficiency. Using the hydrogen equivalent to only one liter of gas, they were able to travel 5,385 km. And the only waste product was water.

Editor's note: Corrin Funnell will be taking a short break from his "Science Factor" series to work on research. Learning Post looks forward to printing future science articles by him.

Corrin Funnell is a laser physicist with a specialty in laser spectroscopy. He has taught in the UK, Egypt, at Thailand's own Harrow International School, where he became head of the physics department. Currently, he is head of Physics at Island School, Hong Kong.