|MadSci Network: Engineering|
Greetings: There are many types of engines for doing work and they all have one thing in common, they convert high temperature liquid, solid or gas materials into low temperature liquid, solid or gas materials and extract power to do work in the process. These processes are based in the laws of THERMODYNAMICS. Generally, the greater the difference between the high and low temperatures, the greater will be the useful power output and efficiency of the engine. Engines that run on gasoline, methanol and diesel fuels are called internal combustion engines (ICE) and they use the rapid explosion, heating and expansion of a compressed fuel air mixture in an enclosed cylinder to drive a piston downward during the power stroke. Currently internal combustion engines have a number of advantages over external combustion engines with the fuel being part of the heating process being a major advantage. Steam engines are external combustion engines (ECE) and they use an external fuel combustion process to convert liquid water to high-pressure, high-temperature steam in a boiler. The high-pressure, high temperature steam is then transferred into the cylinder to drive the piston during the power stroke. However, a steam generating boiler and heater also have to be added to the vehicle to run an ECE engine. Because steam engines run at lower pressure and temperature differences than ICEs, they use larger diameter pistons to produce the same amount of drive power and are less efficient. Your question suggests that it might be possible to use a flash boiler concept for an ECE. An atomizer can be used to convert liquid water to water vapor before heating; however, delivering enough energy to convert the water vapor in a cylinder to super heated steam, about 33 times per second, for a 2000 revolution per minute (RPM) engine, would be a difficult task. A spark plug in an ICE is designed to ignite an explosion which then heats the fuel air mixture in a few milliseconds as the explosion fills the cylinder head. A flash heater would have to heat a water vapor mixture fast enough to produce high pressure steam 33 times per second and the heat must spread by convection rather than explosion throughout the cylinder volume. Two alternatives for flash heating water vapor to steam in an ECE come to mind. These techniques have been studied to possibly replace spark plugs in future ICE engines. One is microwave heating similar to microwave ovens and the second is laser heating of the fuel air mixture as your question suggests. ICEs with laser ignition have been demonstrated using a laser beam focused inside the cylinder head through a quartz window in place of the spark plug. A focussed, pulsed laser can easily reach a temperature to ignite a fuel air mixture; however, here again the ignition of the complete fuel air mixture requires an explosion to fill the entire cylinder head. Microwave heating is probably a more viable concept than laser heating for steam engines. It turns out that water vapor has a molecular resonance at a microwave frequency near 25,000 Megahertz (abbreviated MHz - 25,000 million cycles per second) with a wavelength of 1.2 cm (0.5 inches). This means that water vapor is more efficiently heated at this frequency because a resonant vibration process occurs between the hydrogen and oxygen atoms in water molecules. Microwave energy at the resonance wave length can be efficiently transmitted directly into a cylinder head through a quartz window in place of a spark plug and the entire volume would be flash heated just as a microwave oven heats an entire cup of liquid. Using the cylinder as the flash heating container might actually make this more of an ICE process. The major problem with both microwave and laser flash heating is in achieving the ammount of radiation power necessary to flash heat water vapor to steam. It takes a typical 1000 watt microwave oven used in our kitchens many minutes to heat a cup of water to steam. To accomplish this 33 times per second for a large cylinder would require 100 kilowatts to a Megawatts (million watts) or more of microwave or laser power. Today, there are large microwave and laser transmitters the size of an automobile that operate at these power levels; however, the over all conversion efficiency from a battery to microwave or laser energy for these systems is far less than 30%. Laser diodes with power conversion efficiencies greater than 50% are being developed, however they currently generate only a few watts of power. Recently our laboratory was able to generate a record 1000 watts of continuous laser power using a large number of laser diodes to pump (excite resonances) in a pencil sized YAG laser crystal; however, the over all efficiency from battery power to light power for this laser is less than 30%. Also, we have to get rid of 70% of the total input power (3300 watts) as waste heat. This waste heat might be used to preheat the water vapor before it is injected into the cylinder to improve the over all efficiency of a steam engine. Molecular resonance effects have been used in MASERS (microwave amplifiers) and LASERS (light amplifiers) since the 1950s and 60s. More recently magnetic resonance imaging (MRI) and other quantum resonance effects have been used at very low power levels for medical applications. Using molecular and atomic resonances for heating at high power levels has been studied for thermonuclear fusion power generating applications at the national laboratories using huge building sized lasers; however, this technology has not yet reached break even operation were the power required for operation is less than the power generated by the reaction. In conclusion, microwave or laser systems are still to large and inefficient to quickly produce large amounts of steam. However, when considering the environment it is useful to calculate the over all efficiency of the total process to operate a motor vehicle, including the power required to obtain and deliver the fuel. Also, we must consider the waste products resulting from the operations. Using all these considerations and new molecular and atomic resonance techniques, we may be able to make water/steam or hydrogen/oxygen fueled vehicles a viable technology in the future. Best regards, Your Mad Scientist Adrian Popa
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