An ENGINE is: 'A power machine; a locomotive; a contrvance' (Blackie). For MYNET will use engine to mean the motive power source for a vehicle, or other contrivance. 'Locomtive' is a more modern term for the seperate traction vehicle used by railway trains.
Modern engines began with steam power used for pumpling, railway locomotives, ships and boats beginning in the early 1800's. The dominant engine for highway vehicles for the 1900's has been the liquid fuelled internal combustion engine. The search for a lower quantity and less harmful emissions suggests that these engines may be gradually replaced by electric motors supplied by storage batteries, fuel cells, or other sources of energy.
The future engine for transport vehicles may make a major shift as fuel cell, or other hydrogen based technology improves. The push to reduce the production of Green House Gases, notably CO2 may accelerate the replacement of the familiar engines of the 20th century.
Closely related to transport vehicle propulsion systems is the technology used to supply stationary power. The early development of steam power was prompted by the need for pumping where wind and water power was not available or convenient.
Mobile power developed from the stationary power. Stationary power at the end of the 20th century is dominated by centrally generated electricity distributed by high voltage alternating current. It should not be forgotten that a great deal of the energy used for domestic and other purposes however continues to be from direct combustion of carbon and hydro carbon fuels.
The chemical combination of the carbon content of a fuel and oxygen, i.e, burning produces heat, carbon dioxide (or carbon monoxide if the combustion is not complete). Carbon dioxide is now considered as one of the greenhouse gases. The greenhouse gases are alleged to contribute to global warming. How mankind treats this situation may well change how much of the current stationary and mobile power is produced and consumed.
We are all somewhat familiar with the current 'engine' used in cars and trucks. These are now mostly liquid petroleum (gasoline, diesel oil, or some type of gas or alcohol) fueled internal combustion piston engines.
Modern large and high speed aircraft use mosly liquid petroleum turbine and turbojet engines. Small commercial and private aircraft continue to use gasoline piston engines that have proven less costly to construct. The move from piston engines began during WWII in the 1940's and was prompted by the search for higher speeds at practical levels of fuel consumption.
WWII and subsequent military initives has lead to renewed interes and development of rocket engines. These have mostly been used for military and space purposes. The major civilian use has been to launch and position the orbital satellites that are essential to modern communication technology Rocket engines are the only way yet devised to achieve the high speeds necessary to achieve escape from surface or near surface gravitational effects. The major transport achievement of rocket engines so far are the space flights including the manned trips to the moon.
Modern ships, railway locomotives, highway tractors, construction machinery and farm tractors use mostly liquid petroleum diesel piston engines. The diesel type of piston engine is more fuel efficient, but usually heavier and more costly. The trade offs between gas, gasoline, and esel piston engines lead to applications where local costs and other circumstances select the type by local optimization. The gasoline engine tends to be simpler, lighter and lesscostly than the diesel.
The means of achieving propulsion is closely related to the type of engine and fuel that can be considered a viable vehicle engine. E.g. the screw propellor was shown to be superior to the paddle wheel for ships. Its use dictates that the engine in a ship produce rather low speed rotary motion of the propellor shaft. This can be achieve either by means of a relatively low rotational speed engine or by a speed changing transmission system. A ship tends to run at mostly constant speed and the propulsion force required is relatively steady so that there is usually only one set of forward and reverse gearubg required. Speed change is achieved by changing engine speed.
The most constant speed engines are required for stationary electric power generation where alternating current frequency is controlled so closely that frequency snsitve machines like electric clocks will keep accurate time over extended periods.
Highway vehicles are at the other end of the variation spectrum in comparison with stationary electric power generation. They operate in a variety of speed and torque requirement regiemes. Some of the variation can be handled by the engine, but a suitable speed/torque transmission system must also be available. Power output is directly related to engine rotational speed and shaft torque.
For piston engines, output torque can be related to piston area, crank arm length and cylinder mean effective pressure. If these are held constant then engine size can be reduced by increasing rotational speed. The engine is a significant portion of the total mass of a passenger car. Reducing the mass reduces the power requirements which reduces fuel consumption. Passenger cars continue to become lighter, their engines smaller and operate at higher speeds as the search for better fuel efficiecy and reduced emissions at affordable prices continues. To deal with the desired range of torque and speed variation the required number of transmission gear ranges continue to increase.
A modern highway tractor illustrates the high end of the practial number of gear ratios that can be used. Many such tractors have from ten to 18 speeds forward. The only vehicles with equal or more available gear ratios are modern bicycles for use on a variety of terrain.
For vehicle propulsion the most important are DC and AC electric motors.
During the mid and late 1970's concern developed over the supply of suitable liquid petroleum, the essential fuel for most of these engines. An extensive search for alternative fuels and other types of engines began. Since then world petroleum prices and supplies appear to have stabilized but the problems anticipated in the 70's have not gone away. The whole fabric of modern life depends on transportatio using liquid petroleum fuel. There are several alternatives but none as generally attractive. Combustible gas is the best.
The transportation revolution began with the successful application of steam piston engines to ship and railway propulsion. The earliest steam engines were 'stationary' because of their mass, boiler and combustion requirements. Making stem engines mobile ment increasing their power to mass ratio and thermal efficiency. Steam power developed rapidly and persisted in ships and railways until about 1950. The advantage of steam for these applications was the ability to use solid fuel. Coal was the favorite because of its high energy to mass ratio. Steam turbines have high power to mass ratios and replaced piston engines where high output is important. Much of our electric power generation uses steam turbines.Until about 1950 the gasoline fueled piston engine gave the most favorable power, weight, cost combination. Gas turbine technology began development for military aircraft and is ongoing. Gas turbines have a special application in aircraft where high exhaust volumes and velocities can be utilized directly for propulsion. It has been more difficult to apply gas turbines for surface modes, and their use has not developed as expected. Use of fuel cells for direct generation of electricity may effect a change in way electric power is applied.
SPECIFIC FUEL WEIGHT CONSUMPTION #/HP #/HP-HR NON-REGENERATIVE GAS TURBINE 1 1.00 GASOLINE ENGINE 2 .45 REGENERATIVE GAS TURBINE 2 .55 DIESEL 6 .40 FREE PISTON 7 .60 STEAM TURBINE 8 1.00 STIRLING ENGINE 8 .45 DIESEL-ELECTRIC +ELECTRIC MOTORS 18 .45 FUEL CELL+ELECTRIC MOTORS 60 .10There has been improvement in the above, especially with diesels and Fuel Cells However the gasoline engine continues to be a very strong performer because of its cost per unit of power output. The latest in passenger car powerplants developments are in the use of hybrid mixtures of fosssil fueled small engines coupled with bateries and electric motors. Electric motor powered vehicles have improved considerably because of battery improvement. Many are counting on Fuel cell improvements to provide the required electric supply for the future automotive engines. Considerable motivation for improvement in specific fuel consumption and the switch to higher hydrogen content fuels is provided by efforts to reduce Green House Gas Emissions.
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