Engine design is at the confluence of three factors: concerns about how car emissions will affect the environment; rising gas prices and the need to conserve fossil fuel resources; and the realization that the hydrogen-powered car -- be it powered by a hydrogen fuel cell or by hydrogen internal combustion -- will not deliver on its promise in the near future. As a result, many engineers are giving more interest to improving the internal combustion engine.
Photo courtesy Quasiturbine.com
Quasiturbine engine. See more images of engines.
The Quasiturbine engine, patented in 1996, is just such an improvement. In this article, we'll introduce the Quasiturbine engine and answer the following questions:
- Where did the idea for the engine come from?
- What are the parts of the Quasiturbine engine?
- How does the Quasiturbine engine work?
- How does it compare in performance to other internal combustion engines?
Let's get started by looking at some engine basics.
To see how a Quasiturbine engine works, you need to understand some engine basics.
The basic principle behind any internal combustion engine is simple: If you put a tiny amount of air and high-energy fuel (like gasoline) in a small, enclosed space and ignite it, the gas expands rapidly, releasing an incredible amount of energy.
The ultimate goal of an engine is to convert the energy of this expanding gas into a rotary (spinning) motion. In the case of car engines, the specific goal is to rotate a driveshaft rapidly. The driveshaft is connected to various components that pass the rotating motion onto the car's wheels.
To harness the energy of expanding gas in this way, an engine must cycle through a set of events that causes many tiny gas explosions. In this combustion cycle, the engine must:
- Let a mixture of fuel and air into a chamber
- Compress the fuel and air
- Ignite the fuel to create an explosion
- Release the exhaust (think of it as the by-product of the explosion)
Then the cycle starts all over again.
How Engines Work explains in detail how this works in conventional piston engine. Essentially, the combustion cycle pushes a piston up and down, which rotates the drive shaft by way of a crankshaft.
While the piston engine is the most common type found in cars, the Quasiturbine engine operates more like a rotary engine. Instead of using piston like a typical car engine, a rotary engine uses a triangular rotor to achieve the combustion cycle. The pressure of combustion is contained in a chamber formed by part of the housing on one side and the face of the triangular rotor on the other side.
The path of the rotor keeps each of the three rotor peaks in contact with the housing, creating three separate volumes of gas. As the rotor moves around the chamber, each of the three volumes of gas alternately expands and contracts. It is this expansion and contraction that draws air and fuel into the engine, compresses it, makes useful power as the gases expand and then expels the exhaust. (See How Rotary Engines Work for more information).
In the next few sections, we'll see how the Quasiturbine takes the idea of a rotary engine even further.
The Saint-Hilaire family first patented the Quasiturbine combustion engine in 1996. The Quasiturbine concept resulted from research that began with an intense evaluation of all engine concepts to note advantages, disadvantages and opportunities for improvement. During this exploratory process, the Saint-Hilaire team came to realize that a unique engine solution would be one that made improvements to the standard Wankel, or rotary, engine.
Like rotary engines, the Quasiturbine engine is based on a rotor-and-housing design. But instead of three blades, the Quasiturbine rotor has four elements chained together, with combustion chambers located between each element and the walls of the housing.
Photo courtesy Quasiturbine.com
Simple Quasiturbine design
The four-sided rotor is what sets the Quasiturbine apart from the Wankel. There are actually two different ways to configure this design -- one with carriages and one without carriages. As we'll see, a carriage, in this case, is just a simple machine piece.
First, let's look at the components of simpler Quasiturbine model -- the version without carriages.
The simpler Quasiturbine model looks very much like a traditional rotary engine: A rotor turns inside a nearly oval-shaped housing. Notice, however, that the Quasiturbine rotor has four elements instead of three. The sides of the rotor seal against the sides of the housing, and the corners of the rotor seal against the inner periphery, dividing it into four chambers.
In a piston engine, one complete four-stroke cycle produces two complete revolutions of the crankshaft (see How Car Engines Work: Internal Combustion). That means the power output of a piston engine is half a power stroke per one piston revolution.
A Quasiturbine engine, on the other hand, doesn't need pistons. Instead, the four strokes of a typical piston engine are arranged sequentially around the oval housing. There's no need for the crankshaft to perform the rotary conversion.
This animated graphic identifies each cycle. Notice that in this illustration the spark plug is located in one of the housing ports.
In this basic model, it's very easy to see the four cycles of internal combustion:
- Intake, which draws in a mixture of fuel and air
- Compression, which squeezes the fuel-air mixture into a smaller volume
- Combustion, which uses a spark from a spark plug to ignite the fuel
- Exhaust, which expels waste gases (the byproducts of combustion) from the engine compartment
Quasiturbine engines with carriages work on the same basic idea as this simple design, with added design modifications that allow for photo-detonation. Photo-detonation is a superior combustion mode that requires more compression and greater sturdiness than piston or rotary engines can provide. Now, let's see what this combustion mode is all about.
Internal combustion engines fall into four categories based on how well air and fuel are mixed together in the combustion chamber and how the fuel is ignited. Type I includes engines in which the air and fuel mix thoroughly to form what is called a homogenous mixture. When a spark ignites the fuel, a hot flame sweeps through the mixture, burning the fuel as it goes. This, of course, is the gasoline engine.
Gasoline Direct-injection (GDI) Engine
|Pressure-heated Self-ignition||Type IV
Type II -- a gasoline-direct injection engine -- uses partially mixed fuel and air (i.e., a heterogeneous mixture) that is injected directly into the cylinder rather than into an intake port. A spark plug then ignites the mixture, burning more of the fuel and creating less waste.
In Type III, air and fuel are only partially mixed in the combustion chamber. This heterogeneous mixture is then compressed, which causes the temperature to rise until self-ignition takes place. A diesel engine operates in this fashion.
Finally, in Type IV, the best attributes of gasoline and diesel engines are combined. A premixed fuel-air charge undergoes tremendous compression until the fuel self-ignites. This is what happens in a photo-detonation engine, and because it employs a homogenous charge and compression ignition, it is often described as an HCCI engine. HCCI (Homogeneous Charge Compression Ignition) combustion results in virtually no emissions and superior fuel efficiency. This is because photo-detonation engines completely combust the fuel, leaving behind no hydrocarbons to be treated by a catalytic converter or simply expelled into the air.
Source: Green Car Congress
Of course, the high pressure required for photo-detonation puts a significant amount of stress on the engine itself. Piston engines can't withstand the violent force of the detonation. And traditional rotary engines such as the Wankel, which have longer combustion chambers that limit the amount of compression they can achieve, are incapable of producing the high-pressure environment necessary for photo-detonation to occur.
Enter the Quasiturbine with carriages. Only this design is strong enough and compact enough to withstand the force of photo-detonation and allow for the higher compression ratio necessary for pressure-heated self-ignition.
In the next section, we'll look at the major components of this design.
Quasiturbine with CarriagesEven with its added complexity, the Quasiturbine engine with carriages has a relatively simple design. Each part is described below.
The housing (stator), which is a near oval known as the "Saint-Hilaire skating rink," forms the cavity in which the rotor rotates. The housing contains four ports:
- A port where the spark plug normally sits (the spark plug can also be placed in the housing cover -- see below).
- A port that is closed with a removable plug.
- A port for the intake of air.
- An exhaust port used to release the waste gases of combustion.
The housing is enclosed on each side by two covers. The covers have three ports of their own, allowing for maximum flexibility in how the engine is configured. For example, one port can serve as an intake from a conventional carburetor or be fitted with a gas or diesel injector, while another can serve as an alternate location for a spark plug. One of the three ports is a large outlet for exhaust gasses.
How the various ports are used depends on whether the automotive engineer wants a traditional internal combustion engine or one that delivers the super-high compression required of photo-detonation.
The rotor, made of four blades, replaces the pistons of a typical internal combustion engine. Each blade has a filler tip and traction slots to receive the coupling arms. A pivot forms the end of each blade. The job of the pivot is to join one blade to the next and to form a connection between the blade and the rocking carriages. There are four rocking carriages total, one for each blade. Each carriage is free to rotate around the same pivot so that it remains in contact with the inner wall of the housing at all times.
Each carriage works closely with two wheels, which means there are eight wheels altogether. The wheels enable the rotor to roll smoothly on the contoured surface of the housing wall and are made wide to reduce pressure at the point of contact.
The Quasiturbine engine doesn't need a central shaft to operate; but of course, a car requires an output shaft to transfer power from the engine to the wheels. The output shaft is connected to the rotor by two coupling arms, which fit into traction slots, and four arm braces.
When you put all of the parts together, the engine looks like this:
Photo courtesy Quasiturbine.com
Quasiturbine engine with carriages
Notice that the Quasiturbine engine has none of the intricate parts of a typical piston engine. It has no crankshaft, valves, pistons, push rods, rockers or cams. And because the rotor blades "ride" on the carriages and wheels, there is little friction, which means oil and an oil pan are unnecessary.
Now that we've looked at the major components of the Quasiturbine with carriages, let's see how everything comes together. This animation illustrates the combustion cycle:
Photo courtesy Quasiturbine.com
The first thing you'll notice is how the rotor blades, as they turn, change the volume of the chambers. First the volume increases, which allows the fuel-air mixture to expand. Then the volume decreases, which compresses the mixture into a smaller space.
The second thing you'll notice is how one combustion stroke is ending right when the next combustion stroke is ready to fire. By making a small channel along the internal housing wall next to the spark plug, a small amount of hot gas is allowed to flow back to the next ready-to-fire combustion chamber when each of the carriage seals passes over the channel. The result is continuous combustion, just like in the airplane gas turbine!
What all this amounts to in the Quasiturbine engine is increased efficiency and performance. The four chambers produce two consecutive circuits. The first circuit is used to compress and expand during combustion. The second is used to expel exhaust and intake air. In one revolution of the rotor, four power strokes are created. That's eight times more than a typical piston engine! Even a Wankel engine, which produces three power strokes per rotor revolution, can't match the performance of a Quasiturbine.
Quasiturbines: Advantages and Disadvantages
Obviously, the increased power output of the Quasiturbine engine makes it superior to Wankel and piston engines, but it has also solved many of the problems presented by the Wankel. For example, the Wankel engines leads to incomplete combustion of the fuel-air mixture, with the remaining unburned hydrocarbons released into the exhaust. The Quasiturbine engine overcomes this problem with a combustion chamber that is 30 percent less elongated. This means that the fuel-air mixture in the quasiturbine experiences a greater compression and a more complete burn. It also means that, with less fuel going unburned, the Quasiturbine increases fuel efficiency dramatically.
Other significant advantages of the Quasiturbine include:
- Zero vibration because the engine is perfectly balanced
- Faster acceleration without a flywheel
- Higher torque at lower rpm
- Nearly oil-free operation
- Less noise
- Complete flexibility to operate completely submerged or in any orientation, even upside-down
- Fewer moving parts for less wear and tear
Photo courtesy Quasiturbine.com
Considering the modern internal combustion engine was invented by Karl Benz in 1886 and has enjoyed almost 120 years of design refinements, the Quasiturbine engine is still in its infancy. The engine is not used in any real-world applications that would test its suitability as a replacement for the piston engine (or the rotary engine, for that matter). It is still in its prototype phase -- the best look anyone has gotten so far is when it was demonstrated on a go-kart in 2004. The Quasiturbine may not be a competitive engine technology for decades.
In the future, however, you will likely see the Quasiturbine used in more than just your car. Because the central engine area is voluminous and requires no central shaft, it can accommodate generators, propellers and other output devices, making it an ideal engine to power chain saws, powered parachutes, snowmobiles, air compressors, ship propulsion systems and electric power plants.
For more information on the Quasiturbine engine, other engine types and related topics, check out the links on the next page.
Did cars ever have external combustion engines? Find out if external combustion engines have ever being used to power automobiles at HowStuffWorks.
Related HowStuffWorks Articles
- How Car Engines Work
- How Diesel Engines Work
- How Gas Turbine Engines Work
- How HEMI Engines Work
- How Radial Engines Work
- How Rotary Engines Work
- How Stirling Engines Work
More Great Links
- U.S. Patent #6,164,263: Quasiturbine AC (Quasiturbine zero vibration-continuous combustion rotary engine compressor or pump)
- MIT: Hydrogen vehicle won't be viable soon, study says
- Ashley, Steven. 2001. A low-pollution engine solution. Scientific American. June.
- Bode, Dave. 2000. An engine for the new millennium? FindArticles.com. April.
- Physics Daily: The Physics Encyclopedia, s.v. "quasiturbine,"
http://www.physicsdaily.com/physics/Quasiturbine (accessed May 14, 2005).
- Physics Daily: The Physics Encyclopedia, s.v. "Wankel engine,"
http://www.physicsdaily.com/physics/Wankel_engine (accessed May 14, 2005).
- Quasiturbine.com, http://www.quasiturbine.com/EIndex.htm
- Stauffer, Nancy. 2003. Hydrogen vehicle won't be viable soon,
study says. Massachusetts Institute of Technology News Office. March 5.
- Stokes, Myron D. 2003. Quantum parallel: The Saint-Hilaire "quasiturbine"
as the basis for a simultaneous paradigm shift in vehicle propulsion systems. December 15.
- Tse, Lawrence. 2003. Quasiturbine: Photo-detonation engine for
optimum environmental benefits. Visionengineer.com. June 8.
- U.S. Patent Office web site, Quasiturbine patent application.
Patent # 6,659,065.
- Wright, Michael and Mukul Patel, eds. 2000.
Scientific American: How things work today.
New York: Crown Publishers.