时间:2018-10-09 13:53 来源:http://www.lunwentong.com/ 作者:佚名 点击:次
When engineers face the challenge of combating fuel efficiency, many subjects come to mind. Alternative fuels, drive-train configuration, weight, cost, time, and reliability are just a few factors concerning fuel efficiency. There are various ways to tackle fuel efficiency, one being the engine of the car. Most automobiles today are powered by the reciprocal piston form of the internal combustion engine, which utilizes pistons that travel in a linear motion to turn a crankshaft. Other forms of internal combustion engines include the rotary engine, jet engine, and rockets, all of which have a low overall efficiency in converting chemical energy into mechanical energy. This is caused by a tremendous amount of energy, which is converted to heat and friction rather than mechanical energy. What if these negative factors could be greatly reduced if not eliminated? Today's area of focus is improving the power plant, which will propel the vehicle of tomorrow. This is a good approach at achieving a short-term solution for petroleum consumption, but a fresh start may be required to achieve the perfect solution to fuel efficiency. I have chosen to focus on the following power plants; Quasiturbine, HCCI, clean diesel, and Atkinson, which may prove to be the key technologies that will revolutionize the automotive industry forever. However, only one technology may win.
Mankind has been improving the internal combustion engine for over 120 years, yet not much has changed in the overall design. '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.' (Harris) Today's cars are propelled by the conventional piston engine, which rely on a series of pistons, usually in a V-four, six or eight configuration, that move up and down to transmit energy to a crankshaft. Some newer conventional engine technologies include Atkinson and HCCI. There have been many improvements made to the design such as better porting, increased valve duration, electronic fuel injection, and harmonic balancing, but the sinusoidal crankshaft motion remains. Sinusoidal motion relates to the pulsating energy within an engine. With the piston configuration, most energy is transferred to the stop and go motion of the piston. Unfortunately, it is impossible to create a constant power cycle within a piston engine. 'Only 20% of the cycle is power, which results in a power lag 80% of the time which is spent on compressing gasses and a heavy flywheel must compensate for the lag.' (QT Theory Piston Differences) This is where a continuous combustion would be ideal, as found in the Quasiturbine engine.
The Saint-Hilaire family created the Quasiturbine engine in 1996 after intense research and development. This engine is similar to the Wankel rotary engine in that it involves a rotor and housing, but it utilizes a four-blade carriage mechanism compared to the Wankel's three. The four blades rotate about an oval housing with a chain-like motion. At each pivot there is a carriage which houses two wheels, allowing the engine to operate with little to no oil since friction is almost absent. The eight wheels make a tight seal against the housing and create four sealed chambers in which the intake, compression, combustion, and exhaust cycles can occur. 'In a piston engine, one complete four-stroke cycle produces two complete revolutions of the crankshaft. 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, does not need pistons. Instead, the four strokes of a typical piston engine are arranged sequentially around the oval housing. There is no need for the crankshaft to perform the rotary conversion, yet an output shaft is attached to the rotor by two coupling shafts so it can power an automobile.' (Harris)
Most, if not all gasoline engines use an electrical ignition source. This process produces a flame front which results in an unburned fuel mixture at high rpm, thus reducing the engines efficiency. To combat this, Rudolf Diesel created a piston engine which ignited fuel using high compression. This proved to be more efficient than gasoline engines; however, more pollutants resulted from unburned diesel fuel. There have been recent advancements in Diesel after treatment systems like urea injection and advanced catalyst reduction, but that adds weight and cost to the vehicle. Like the diesel, the Quasiturbine engine can run without an ignition source. Unlike diesels, the QT can operate on gas. The advantage of this high compression cycle results in a more complete combustion without the risks of detonation, thus reducing emissions and eliminating the need for complex after treatment systems. Detonation is premature ignition within piston engines and can cause severe damage. Interestingly, fuel is burned well in detonation situations. (QT Theory Piston Differences)
An improved version of the QT engine has been developed which incorporates photo-detonation as an ignition source. Photo-detonation is a process in which a homogenous air/fuel mixture is spontaneously ignited from tremendously high compression. The result is virtually no emissions and superior fuel efficiency. (Harris) This in turn would eliminate the use of a catalytic converter. Photo-detonation places a significant amount of stress on an engine. General Motors has been experimenting with photonic detonation (or HCCI); however, they are testing it on piston engines. These engines were not designed to endure this combustion process as they are susceptible to detonation and as a result, GM has only been successful at sustaining HCCI for short durations within piston engines. HCCI can however, occur in the QT engine because of its strong and compact design, as well as the capability for continuous combustion. (Harris)
Unlike the conventional piston engine, which utilizes one chamber to accomplish all four cycles, the QT has four separate chambers designated for each cycle. Having four chambers allows thermodynamic efficiency as the intake charge is always in a cool region and the combustion cycle occurs in a continuous hot region. This is unable to happen in a piston engine, where the cylinder is hot at the intake charge and cool during the combustion process. These factors result in a lowered efficiency. To maximize efficiency, the Quasiturbine has eight mini chambers which are derived from the four main chambers. The presence of the carriages allows this possibility. Eight chambers create a shorter cycle duration in which a higher RPM can occur. Unfortunately in piston engines, a higher RPM results in a lower efficiency as the flame front limits velocity. The advent of eight chambers also results in eight times the power output when compared to conventional engines. The sparkplug fires once during one revolution in a conventional engine, whereas combustion occurs eight times during one cycle in the QT engine. During this process, one combustion stroke is ending as another is ready to fire. 'A small channel in the housing allows some hot gas into the combustion chamber, which heats the incoming charge to further accomplish photo-detonation.' (Harris) The result is a continuous combustion process much like a jet turbine engine. (QT Theory Piston Differences)
Like the jet engine, the Quasiturbine has a high efficiency. Unlike the jet, the QT is economical for automobile use as it has a varying RPM range. Conventional engines have a varying RPM range, but it is too high for the wheels, which turn on average four to five times slower than the engine. To harvest the engine's power, a gearbox or transmission is required. This reduces the overall efficiency of the vehicle because the gearbox requires energy to operate and creates power surges. The Quasiturbine operates in the 700-1200 RPM range, which is the equivalent of the wheel RPM in an average car. This configuration would be optimal for efficiency because a gearbox is not required to transfer power to the wheels. Furthermore, the QT produces a high torque at low RPM, which is what most driving conditions require. Conventional engines do not operate efficiently at low RPM, which is why a heavy flywheel is required to maintain proper harmonic motion. There is possibility of even eliminating the clutch when the QT is used. This is because the engine can be stopped when the wheels are stopped, but quickly fired up when power is needed. The QT can also operate at a continuously low RPM as the heat from one combustion cycle is used to ignite the next. Rotational mass is greatly reduced with this configuration. (QT Theory Piston Differences)
Weight is a major factor affecting fuel mileage. The engine in most cars makes up 25% of the total weight of the vehicle. This not only reduces the engine efficiency, but the overall performance suffers. The heavy engine must power itself and power the car, which absorbs most of the chemical energy in the fuel. Electric cars, while they can achieve low RPM's as stated earlier, are heavy due to their batteries. This is also one of the reasons why fuel cells are not on the market yet, as they are too bulky. Diesel and gasoline engines are also heavy with respect to their given power output. The Quasiturbine weighs approximately as much as the conventional engine and 1/6th as much as electric power. This factor when combined with the compact design allows for different car configurations in which the overall weight of the car can be significantly reduced. This in turn would tremendously increase the fuel mileage of vehicles. (QT Advantages Efficiency)
Other factors concerning automotive engineers are vibration, noise, and pollution. Since the Quasiturbine engine is perfectly balanced, there is no resulting vibration. Vibration and noise are both reduced by the gradual evacuation of gasses and a greater angular displacement. Furthermore, the expansion of gasses is split into four which allows for smoother operation. The four chambers allow a shorter confinement time for gasses, which will help to eliminate NOx emissions. High pressure, temperature and confinement times all lead to NOx emissions. The Quasiturbine expansion starts quicker than other engines which produce lower initial temperatures and pressures and the confinement time is greatly reduced. The overall result is a smoother, quieter, and cleaner engine. (QT Theory Engine Problematic)
Rising fuel costs are a concern for everyone. With the hope to reduce and eventually eliminate the dependence on oil, alternative fuels have become a major interest among auto manufactures. The Quasiturbine is able to efficiently operate on methanol, gas, diesel, hydrogen, and even water with simple modifications. An earlier expansion process means an end to fuel additives to prevent detonation and a beginning to new fuel uses. 'The Quasiturbine meets the fundamental? criteria imposed by the 'hydrogen' engine of the future (cold intake area, stratified intake, reduced confinement time, low sensitivity to detonation, less pollutant, robust and energy efficiency), and even surpasses the Wankel in this respect, since the intakes are separated by 3 strokes instead of two. Frequent instabilities in the combustion of hydrogen should not appreciably affect the Quasiturbine, as it is not sensitive to detonation.' (QT Theory Piston Differences) Water injection can be used to operate the QT like the steam engine, but without the risk of explosion. Liquid water can be directly injected into a hot Quasiturbine where it will flash steam and propel the engine. This process would be ideal to use in a fuel conversion mode where the combustible fuel would be shut off when the engine is hot enough to operate on water. Then when the temperature cools, the fuel could be introduced again. These factors could greatly reduce, if not eliminate, our dependency on foreign oil.
So far, it seems that the Quasiturbine may be the perfect solution over HCCI, clean Diesel and gasoline, for eliminating America's dependency on oil. This however may not be the case. Although the proposed engine may seem to be perfect, it does have some shortcomings. One such factor is the infancy of the technology. Mankind has been perfecting the I.C.E. for the past 100 years, and the Quasiturbine was unveiled in 1996. This infancy is shared with the hydrogen fuel cell, with respect to a lack of technological advancements which make the proposed solutions a poor replacement for current technologies. Clean diesel is deemed by many sources to be the next advancement in power train technology; however, the dependency on oil remains. This dependency is also true for HCCI and Atkinson engines, as they are petroleum based. The plus for such engines however, are the ease of viability and implementation for automotive use at a reasonable price. Electric hybrids are a popular sector of the auto market today, but battery technology is not advanced enough to sustain long-distance commutes. As far as design and aesthetic qualities, the Quasiturbine beats all competition with its simple, lightweight design and excellent efficiency capabilities.
Overall, we think the Quasiturbine engine has a great possibility to revolutionize the automotive industry and reduce our dependence on foreign oil. The design is an environmentally friendly concept, which ties in with helping to reduce global warming. Photo-detonation, while a new concept, has great potential to solve emissions concerns for the future. The main fallback of the Quasiturbine seems to be the infancy of its development and unknown development costs. The world needs a quick solution and the Quasiturbine may not be ready for immediate use, however, the QT would make a great long-term solution. This invention appears to have solved or improved upon the shortcomings of the conventional engine used today. Weight savings, alternative fuels, noise reduction, anti-vibration, and above all, reliability have all been incorporated into this new engine. The possibilities are endless. Sure, mankind has made vast improvements on the piston engines, especially in the Diesel sector where high compression leads to greater efficiency, but the downfall is oil dependency. The Quasiturbine solves all of the current issues concerning the internal combustion engine and increases the market for alternative fuels. This will ultimately eliminate our dependence on fossil fuels and generate a cleaner, quieter, and reliable power solution for the vehicles of tomorrow.