What is the purpose of all this sophisticated wizardry? Quite simply, to save fuel. The Prius I drove boasts a fuel-consumption rate of four litres per 100 kilometres for city driving

In the new Prius, the small dashboard-mounted computer screen shows the driver which power source is being used and the car's fuel-consumption rate at any given moment and provides a wealth of other information. Additional features of the vehicle include regenerative braking, which uses energy produced when brakes are applied to help recharge the battery; an electronic sensor that "recognizes" the driver and eliminates the need for an ignition key; and a "gearless" transmission system – shifting is only required between forward and reverse.

What is the purpose of all this sophisticated wizardry? Quite simply, to save fuel. The Prius I drove boasts a fuel-consumption rate of four litres per 100 kilometres for city driving and 4.2 litres per 100 kilometres on the highway. And not only is the fuel-consumption rate almost twice as good as in the average new car, but the better fuel economy for city versus highway driving (a result of the engine shutting off completely, rather than idling, when the car stops) is unique. Equally important is the fact that on an overall distance-travelled basis, the Prius releases only about 10 percent of the exhaust emissions of comparable conventional cars.

Impressive as these statistics are, it's perhaps significant that this "car of the future" still relies on an internal combustion engine as the ultimate source of its energy. As recently as 2001, some automotive experts were predicting the imminent demise of automobiles powered by gasoline- or diesel-fuelled internal combustion engines. These cars would be supplanted, they suggested, by the fuel-cell vehicle, which runs entirely on electricity created on board from hydrogen in stacks of fuel cells. (Advanced membrane technology is used to separate electrons from protons, enabling electricity to be generated with water vapour as the only emission.) At the time, almost every major automobile manufacturer had produced at least one prototype fuel-cell vehicle, and commercial production was thought to be only short years away.

Today, however, many experts believe that it could be several decades before fuel-cell vehicles are common on our roads. In an August 2004 issue of Fortune magazine, Joseph Romm, an author and former U.S. Energy Department official, wrote that hydrogen vehicles would be lucky to get five percent of the market by 2030. And a recent report by the investment firm BMO Nesbitt Burns states that "significant technical and economic barriers are expected to keep fuel-cell vehicles from making significant market penetration until at least 2020."

Those technical and economic barriers include the high cost of fuel cells themselves, difficulties with cold-starting and warm-up times, and most of all, the problem of supplying the necessary hydrogen and delivering it to consumers at the roadside. Hydrogen is the most plentiful element on earth, but it occurs only in compounds with other elements – notably oxygen (as water) or carbon (as natural gas and other hydrocarbons such as gasoline). In its gaseous state, hydrogen is highly volatile – in fact, explosive. So the technical challenges of building infrastructures to produce, transport and use hydrogen safely, reliably and affordably are tremendous and will likely not be resolved quickly.

Automotive and petroleum industry researchers are experimenting with systems to extract hydrogen from gasoline within the vehicle, but again, production on a commercial scale may be a long way off. Many experts believe that fuel cells are much more likely to be used in large-fleet vehicles such as buses and for stationary applications such as industrial and residential power generation than in automobiles.

In the meantime, fuel-efficient and low-emitting hybrids have gone into commercial production, and while they have not exactly taken the market by storm, they have at least been favourably received and may be turning a significant corner. Trade reports note that Toyota sold 1,300 second-generation Prius cars in the 10 months following its introduction, more than the total number of the first-generation version sold since its introduction in 2001. As well, Honda has announced hybrid versions of its popular Civic and Accord lines, Ford has introduced its hybrid Escape model, and other manufacturers are believed to have plans to introduce hybrids.

Exxon Mobil Corporation, Imperial Oil's multinational affiliate, projects that hybrids will account for about one-quarter of new vehicle sales in the United States by 2020. It forecasts that, by far, the majority will be "conventional" single-power-source vehicles with gasoline- or diesel-fuelled internal combustion engines. Which is to say, the internal combustion engine, either in hybrid or traditional vehicles, will likely remain the standard power source for automobiles for a good while yet, as it has been since the first "motor car" took to the roads almost 120 years ago.

"Historically speaking, the internal combustion engine must stand as one of the world's greatest inventions," says Professor Jim Wallace of the department of mechanical and industrial engineering at the University of Toronto. "By dramatically improving the mobility of both people and goods, it changed civilization and society within a very short period. Today, few of us could imagine what our lives would be like if the automobile didn't exist."

Indeed, the car has become central to daily life. More than seven of every 10 North Americans own one, and four of every 10 Europeans. Our cars carry us to work and school, to the supermarket and the doctor, to vacation spots and to family and friends. In some respects, the history of the 20th century could not have unfolded as it did without the automobile and other vehicles powered by the internal combustion engine.

The design of the internal combustion engine – attributed to various individuals, although most commonly to the German inventor Nicolaus Otto – is elegantly simple. In its most common "four-stroke" configuration, combustible gas is introduced through a valve into a cylinder and compressed by a rising piston that is attached to a rotating crankshaft. When the gas is ignited (either by a spark plug in a gasoline engine or spontaneously by pressure in a diesel engine), the resulting explosion drives the piston down the cylinder, which turns the crankshaft. On the return upward stroke, the piston expels the spent gas through an outlet valve. Then, as it starts down again, the piston draws more gas into the cylinder and the cycle is repeated. The more cylinders that are attached to the crankshaft, the greater the amount of power generated.

On an overall distance-travelled basis, the Prius releases only about 10 percent of the exhaust emissions of comparable conventional cars

While powering automobiles and other vehicles has been the most widespread application of the internal combustion engine, it also has many other uses – from boats and airplanes to industrial machinery, pumps, chainsaws and lawnmowers. And, of course, there have been many refinements over the years. Most notably, engineers found that increasing the compression in the combustion chamber generated more power from smaller engines. Yet the internal combustion engine that Otto's fellow German Gottleib Daimler attached to a bicycle frame in 1885 is essentially the same as the engines that power today's automobiles – from the lowest-priced economy car to the most expensive limousine or "muscle car."

Certainly, the car itself has changed, but under the hood, gas is still compressed and ignited and the pistons still go up and down, rotating the crankshaft to deliver power to the wheels.

For most of the 20th century, Professor Wallace notes, advances in vehicle technology focused more on drive trains and other ancillary systems (innovations such as four-wheel hydraulic and disk brakes, independent suspensions, automatic transmissions, limited-slip differentials, radial-ply tires, power-assisted steering and other consumer-friendly features) than on the engine itself. "Probably the most dramatic changes to the engine took place in the mid-1980s with the introduction of microprocessors, which allowed continuous fine tuning of fuel and ignition systems," explains Wallace. A response to new automotive emission standards that required the installation of catalytic converters in exhaust systems, microprocessors (essentially small onboard computers) provided greatly improved control over fuel consumption and emissions while maintaining engine power and performance. Among other things, they allowed closely controlled fuel injection systems to replace the traditional carburetor as the standard method of delivering an air-fuel mixture to the cylinder.

Microprocessors – essentially small onboard computers – provided greatly improved control over fuel consumption and emissions while maintaining engine power and performance

As the internal combustion engine and its fuelling systems evolved, the fuels themselves were required to keep pace. Higher-compression engines required higher-octane gasolines to prevent "knocking" and maintain performance, which led to the use of octane-increasing additives, such as lead. Then, in response to air-quality concerns, lead additives were phased out. Later, "detergent" additives were introduced to keep advanced fuel injection systems clean and functioning. More recently, sulphur levels in gasoline have been drastically reduced to meet the needs of today's more complex emission-control systems, and more stringent sulphur-content standards will soon be applied to diesel fuel.

The combination of reformulated fuels and improved fuelling and exhaust systems has resulted in steady improvements in fuel efficiency – an average of 1.5 percent a year, or more than 30 percent since the early 1980s – and truly dramatic reductions in exhaust emissions of pollutants such as carbon monoxide, sulphates, nitrogen oxides and volatile organic compounds (unburned hydrocarbons) that contribute to smog formation. In fact, a new car today produces less than one percent of the smog-related emissions per kilometre than a comparable new car of the mid-1970s.

David Paterson, vice-president of corporate and environmental affairs for General Motors of Canada, cites some startling data in this respect. "You could drive 37 new Chevy TrailBlazers around the equator and produce fewer emissions than burning a single cord of firewood," Paterson says, adding that using one gallon (3.8 litres) of water-based house paint puts more smog-related substances into the air than driving a Chevy TrailBlazer from Toronto to Vancouver and back again.

Even more promising is a fuelling and combustion technology known as "homogeneous charge compression ignition"or HCCI, which is ... believed to have the potential to improve the fuel economy of internal combustion engines by as much as 30 percent

It's interesting to note, however, that the improved fuel economy of engines has not led to lower fuel consumption overall. "The average fuel consumption per kilometre of new vehicles in North America hasn't improved in 20 years," says Jim Hughes, manager, energy analysis, with Imperial's corporate planning department. "And the simple reason for this is that consumers have been buying larger, more powerful vehicles. Engineering efficiency gains don't necessarily translate into reduced energy consumption."

Hughes's assessment is borne out by the data. Relatively larger and less fuel-efficient sport utility vehicles (SUVs), pickup trucks and minivans now account for about half of all vehicles on the road in Canada. This trend may be changing, however. Automobile industry analysts report that Canadian sales of larger vehicles were significantly lower in the first three-quarters of 2004 than in the previous year, and some manufacturers are planning to introduce smaller, more fuel-efficient SUVs, including hybrid models.

At the same time, the internal combustion engine itself may be poised for further improvements in fuel efficiency. Sherri Stuewer, a manager with ExxonMobil's corporate planning department, points out that although the fuel efficiency of automobile engines has doubled since 1974, there is still a lot of room for improvement. "Engine fuelling systems remain a key focus of our company's research, and some highly promising options are already in development," Stuewer says. "By 2020, the internal combustion engines in new vehicles will almost certainly be significantly more fuel- and energy-efficient than the engines in cars being sold today."

One technical improvement that is offered in some European vehicles is direct injection fuelling. In the microprocessor-controlled fuel injection systems introduced in the 1980s, a computer-determined mixture of fuel and air is injected into an inlet port (basically, a holding chamber at the top of the cylinder) before being drawn into the combustion chamber for compression and ignition. With direct injection, a jet of air and vaporized gas is sprayed through a nozzle directly into the combustion chamber, resulting in more controlled and complete burning, providing greater power and lower emissions.

Even more promising is a fuelling and combustion technology known as "homogeneous charge compression ignition," or HCCI, which is currently under development and believed to have the potential to improve the fuel economy of internal combustion engines by as much as 30 percent. HCCI combines the principles of the traditional gasoline-powered engine with those of the equally well-established diesel-fuelled engine. In a gasoline engine, the vaporized gas in the combustion chamber is ignited by a spark plug. In a diesel engine, the vapour ignites spontaneously, a result of both heat and the pressure created by the piston rising in the cylinder.

Because diesel fuel has a slightly higher "energy density" than gasoline (i.e., more latent energy is contained in each litre), diesel engines are generally more fuel-efficient. On the negative side, diesel engines generally have higher emissions of substances that contribute to smog formation. In an HCCI engine, a homogeneous mixture of vaporized fuel and air is made to ignite spontaneously. In principle, either a gasoline or a diesel engine could be made to operate in HCCI mode. According to Sherri Stuewer, such an engine would perform with the fuel economy of a diesel engine, but with significantly lower emissions. Jim Wallace agrees that the potential for major benefits is there, but cautions that there are some fairly serious technical difficulties to be resolved. "In particular, the timing of spontaneous ignition is highly dependent on both the in-cylinder temperatures and on the fuel composition," he points out. "This presents a challenge to controlling the combustion process and will likely require introduction of engine technology still under development. In addition, the HCCI mode of operation may be limited to just part of an engine's load and speed range by high combustion rates."

Should HCCI and other energy-saving engine technologies prove to be technically and commercially feasible, the benefits to both motorists and the environment could be substantial. "Finding ways to improve the fuel efficiency and emissions performance of vehicles means finding ways to reduce pollution and extend the life of our limited supplies of oil," says Stuewer. "To put this in perspective, if we could improve the efficiency of every new car by just 10 percent, the gasoline saved worldwide over 10 years would be greater than all the gasoline consumed by all the cars in the United States and Canada today."

The potential energy-saving benefits of HCCI and other advancements in internal combustion engine technologies could become further magnified if and when they are incorporated into hybrid vehicles. In fact, ExxonMobil researchers believe that the fuel economy and lower emissions of future hybrids could almost equal those of hydrogen-powered fuel cell vehicles.

Potential benefits of this magnitude provide a powerful incentive for automakers, petroleum companies and governments to support further research and experimentation into improving the efficiency of the internal combustion engine. Moreover, if projections for the future growth of automobile markets around the world prove to be even close to correct, the need becomes more compelling. Consider the following facts.

Worldwide, fewer than 10,000 cars were manufactured in 1900. Today, automakers around the world produce more than 60 million passenger cars and light-duty vehicles such as vans and pickups a year. According to ExxonMobil, there are 235 million automobiles in North America alone, and 230 million in Europe. By 2030, those numbers are projected to rise to 325 million and 270 million, respectively.

Even more startling, huge potential automobile markets – especially in Asia, where the economies of countries such as China and India are rapidly expanding – remain virtually untapped. ExxonMobil projects that with rapid population and economic growth, the number of vehicles in Asia will increase from around 55 million today to an astounding 420 million by 2030.

Exactly what kinds of cars those millions of future motorists will be driving is impossible to predict. Technological breakthroughs are certainly possible, and markets will undoubtedly inspire ingenuity in design and engineering. But it seems very likely that the efficiency, reliability and low cost of the internal combustion engine will keep it a staple of transportation for a good while yet, either in hybrids or as the sole power source. And if the Toyota Prius that I test drove in the fall is any indication of things to come, then for my part, that will be a good thing. If this is the "car of the future," count me in.