It has been said sometime ago that if someone suggested powering our transportation system with gasoline and using internal-combustion engine, they would be laughed off the stage. Gasoline is far too dangerous to handle, and the internal combustion engine is far too inefficient. Well, given a hundred years of refinement and billions of dollars in research, we have a system that works pretty well.
That said, the gasoline engine is facing real problems today. The finite oil supplies in the world will be spread far more thinly with emerging markets primarily in China and India. A new energy source will be needed and likely a new "engine" to use it will be developed. It will be used at least in parallel with the existing gasoline system, if not replace it. Will it be the fuel cell? Possibly.
But in the meantime, the gasoline engine is undergoing some pretty dramatic refinements. The problem with the gasoline engine is that efficiency is in reverse to the way it is almost always used. That means that it is least efficient at low rpm, and that is where the engine is used the most, particularly in traffic.
Why is this? An internal-combustion engine operates by flowing the air and gasoline mixture into the cylinders, burning it, and expelling the result out the exhaust. Anything that restricts that flow, lowers the efficiency. So, why restrict the flow? A throttle plate is needed in the intake flow (manifold) to slow the flow and force the engine to operate at less than maximum rpm. This means that the engine now has to suck the air around the throttle plate, and that is not efficient.
Another flow restriction are the valves in the cylinders that shut the incoming air/gasoline flow off so the engine can burn the gasoline mixture and force the piston down, turning the crankshaft, driving the wheels, then other valves that open to let the waste gases out.
Finally, the restrictions to flow of the waste gases are the catalytic converter and muffler.
All of these systems have had lots of research done to make them do their jobs as well as possible and be as efficient as possible. Note that efficiency not only means economy of fuel consumption, but also power development. Competition in the auto industry means that engines must be both powerful and fuel efficient.
Working from the exhaust to the intake, all that can be said here about the exhaust system is that a lot of work over the years has been done to make sure that the system works very well to clean up the exhaust and make the engine quiet, and at the same time with as little restriction to gas flow as possible. Some study in recent years, however, has been done to make the exhaust "sound good" as well as be quiet enough to meet noise level standards set by many countries.
The engine itself has undergone some very significant changes in the last five years or so. Detail changes like improving lubrication by using expensive synthetic oils has improved fuel economy by a tenth of a mile per gallon or so. Little improvements like that mean a lot when added together, plus they also add up when corporate average fuel economy is concerned for a manufacturer.
There have been significant improvements in the "top end" of the engine. Starting in the seventies, manufacturers have gone to overhead cam engines. GM may stick to pushrod engines, but there is no question that the overhead cam engine is more efficient. If it wasn't, why would Toyota use only overhead cam engines in all their production cars and trucks? GM argues that they use pushrod engines because they are more compact, which is true, but the real reason is that they are cheap to produce. In the past couple of years, the overhead cam engines are being improved even more. One problem with the mechanical design of the internal-combustion engine has been that the valves were opened with camshafts that were linked mechanically to the crankshaft, hence the valves opened at a fixed rotation time regardless of whether the engine was operating at high or low rpm. This was a compromise because the optimum time to open the valves is different (for fuel efficiency and/or power) at low and high rpm. So, adding some cost to the engine resulted in variable valve timing. How this is done is a little different depending on the manufacturer, so they invent an acronym to describe their design, though the result is the same. Note that this acronym is usually the one with multiple "Vs" in it because both "variable" and "valve" start with that letter.
Recognizing that valves should be opened and closed at different times depending on engine conditions has made manufacturers look into ways of eliminating the camshaft completely. In theory, the valves could be opened and closed with a hydraulic or electric (solenoid) system. The hydraulic system has proved to be big, heavy, and expensive. All three are big negatives. The electric system has proven to be the most possible for production, except that it is expensive and noisy. Both those are big negatives as well. This is a difficult engineering problem because valves take a lot of power to open and close due to that big explosion that happens inside the cylinder every time the gasoline explodes. Reliability is an issue here too because that explosion happens billions of times in the life of an engine.
Intake air management has also been engineered differently in the last ten years. Manifolds now often have switchable or variable lengths to optimize air flow at various engine speeds. Also size is sometimes variable for the same reason. BMW has taken a step further by modifying the manifold and varying valve timing to eliminate the throttle plate. That step not only increased fuel economy by some ten percent, but power as well. While this is expensive, watch for other manufacturers to do the same thing, but with different details to avoid BMW patents.
The last topic is the fuel delivery system. At the beginning of time, as far as the internal-combustion engine is concerned, there was the carburetor. That device was refined along the way until it just didn't work well enough for the upcoming emission standards of the later seventies. Modern electronics of the time also contributed to its demise. Electronics made it possible to monitor engine conditions, particularly emissions in the exhaust using an oxygen sensor. That made it possible to engineer a feedback system to correct the incoming fuel content to make the exhaust as clean as possible.
While emissions is an important consideration, the actual mixing of gasoline and air is the most important issue. The carburetor was designed to mix the gasoline into the air flowing down the manifold to the cylinder. Modern carburetors did a pretty good job at high flows, but didn't do so well when the air wasn't flowing quickly (at idle, for example), nor did they respond well to the accelerator pedal changing position quickly.
Fuel injection systems were a considerable improvement. The injectors were designed to squirt gasoline in fine droplets regardless of how much was injected. This is because "how much" was determined by how long the injector squirted, not the pressure. The real engineering issue is where to put the injector so that the air and gasoline is completely mixed before it gets into the cylinder, or at least mixes as it enters the cylinder. All kinds of bad things happen when the gas isn't mixed properly, such as pinging and high emissions. This can be shown when an injector is clogged and doesn't spray evenly. The engine often runs badly.
This system has worked for some time now and is being refined in detail each year. Engineers, however, have looked at how diesel engines work. The fuel is injected directly into the cylinders. Mechanical injection systems for diesels have been used since World War II for cars and trucks. These systems tend to be very reliable, but they have to cope with very high injection pressures. As an aside, diesel engines are more efficient than gasoline engines primarily because they have no throttle plate. The amount of diesel fuel is varied according to throttle position.
Direct injection for gasoline engines is now standard equipment for Audi and Isuzu in the United States. At this point in time, it probably is more costly than the advantages it offers. Still, there must be some pioneers to lead with new technology. I'm confident that others will follow as new engines are designed. It is most interesting that Audi developed this technology originally to make their long distance race engines (read winning Le Mans for three straight years!) more efficient. Time in the pits refueling means less time on the track.
As with diesel engines, the fuel delivery must be done at very high pressures, greater than ten times that used for current-technology "manifold injection". The advantage is that the fuel can be injected in very precise quantities, plus the cylinder itself can be designed for very precise uniform control. This makes the engine produce less emissions and/or greater power.
Safety is an issue with the newer direct-injection system. Engines with carburetors needed fuel delivered at about 5 pounds/square inch (psi). A manifold injection system was considered dangerous because it delivered fuel to the injectors at 100 to 150 psi. A direct-injection system delivers fuel to the cylinders at greater than 1000 psi. A leak at that pressure puts an awful lot of fuel somewhere in a very short time. Making sure that doesn't happen is a primary consideration when engineering a system with direct injection.
So the internal-combustion engine isn't dead yet. A great deal of engineering money is being spent by manufacturers to make sure it doesn't die soon. But the economics of delivering crude oil to a vastly increasing number of customers world wide virtually insures that some other system for powering automobiles will be developed and deployed to us customers fairly soon.
