Internal Combustion Engines. Allan T. Kirkpatrick
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Название: Internal Combustion Engines
Автор: Allan T. Kirkpatrick
Издательство: John Wiley & Sons Limited
Жанр: Физика
isbn: 9781119454557
isbn:
As shown in Figure 1.21, the overhead camshaft acts on both the intake and exhaust valves via rocker arms. The engine has variable valve timing applied to the intake valves with a shift from low‐lift short duration cam lobes to high‐lift long duration cam lobes above 3500 rpm. In the low‐lift short duration cam operation the two intake valves have staggered timing, which creates additional swirl to increase flame propagation and combustion stability. Roller bearings are used on the rocker arms to reduce friction. The clearance volume is formed by an angled pent roof in the cylinder head, with the valves also angled.
Figure 1.21 A variable valve timing mechanism. (Courtesy of Honda Motor Co.)
Heavy‐Duty Truck Diesel Engine
A heavy‐duty truck diesel engine is shown in Figures 1.22. This engine is an inline six‐cylinder turbocharged diesel engine with a 137‐mm bore and 165‐mm stroke for a total displacement of 14.6 L. The rated engine power is 373 kW (500 hp). The compression ratio is 16.5 to 1. The engine has electronically controlled, mechanically actuated fuel injectors, and an overhead camshaft. Note that the cylinder head is flat, with the diesel fuel injector mounted in the center of the combustion chamber. The inlet ports impart a swirl to the air in the combustion chamber to improve mixing with the radial fuel spray.
The top of the piston has a torus‐shaped crater bowl, so that the initial combustion will take place in the piston bowl. The injection nozzles have three to six holes through which the fuel sprays into the piston bowl. The pressure required to spray the diesel fuel into the combustion chamber is of the order of 1000 bar, for adequate spray penetration into the bowl and subsequent atomization of the diesel fuel. The fuel injection pressure is generated by a plunger driven by the camshaft rocker arm.
Figure 1.22 A 5.9 L L6 on‐highway diesel engine. (Courtesy of PriceWebber.)
Stationary Gas Engine
A stationary natural gas engine is shown in Figures 1.23 and 1.24. Typical applications for stationary engines include co‐generation, powering gas compressors, and power generation. The engine shown in Figure 1.23 is an in‐line eight‐cylinder turbocharged engine, with rated power of 1200 kW, bore of 240 mm, and stroke of 260 mm for a total displacement of 94 L. The compression ratio is 10.9:1. This type of engine is designed to operate at a constant speed condition, typically 1200 rpm. Each cylinder has two intake and two exhaust valves. The piston has a combustion bowl with a deep dish concentrated near the center of the piston, so most of the clearance volume is in the piston bowl.
Since natural gas engines are operated lean to reduce nitrogen oxides (
Figure 1.23 A 94 L L8 stationary natural gas engine. (Courtesy of Cooper Energy Services, Inc.)
Figure 1.24 Cutaway view of 94 L L8 stationary natural gas engine. (Courtesy of Cooper Energy Services, Inc.)
1.7 Alternative Powertrain Technology
In this section, alternative powertrain technology, including electric motors, fuel cells, and gas turbines, are discussed in terms of a particular application where they have some advantage over the internal combustion engine.
Electric Motors
Electric motors compete with internal combustion engines in the range of powers less than about 500 kW. Driven by the need to adopt low‐carbon technology both for
Electric vehicles have a number of advantages over internal combustion vehicles. Electric vehicles are quiet, have lower vibration levels, and cost less to operate, about 1 cent per mile versus 10 cents per mile for internal combustion vehicles. Electric motors have been developed that have high torque‐speed characteristics superior to those of internal combustion engines, and also provide up to 150 kW per wheel. Most of the electric motors currently used in hybrid and electric vehicles are brushless DC motors, with rotor‐mounted permanent magnets. However, use of AC induction motors, in which the rotating magnetic field is produced by electric currents in the stator, is increasing due to their lower cost, and less complex incorporation into the engine powertrain. Electric motor performance maps that contain contours of motor efficiency on a torque‐speed plane are used to choose electric motors for vehicular applications.
Proponents of electric vehicles point out that almost any fuel, solar photovoltaic panels, or wind turbines can be used to generate the electricity used by an electric vehicle, reducing dependence on fossil fuels. There would be no local fossil fuel exhaust emissions emitted by the electric vehicle in an urban environment. However, if the electricity is generated by a power plant using coal as a fuel, the air pollution generated by the coal power plant would negate the air‐quality advantage of the electric vehicle.
The main problem with electric vehicles is the batteries used for energy storage. It is generally recognized that a breakthrough in battery technology is required if electric vehicles are to become a significant part of the automotive fleet. Battery packs for vehicles are generally assembled from groups of individual lithium ion batteries, with a total mass of about 3500 kg, and have a life span of about 5 years. The battery pack capacity for automobiles varies from about 25–100 kWh, and fully electric urban buses are equipped with batteries with capacities from 600 to 1000 kWh. The electric vehicles that have been built to date have a limited range of only 100–200 mi (160–320 km), on the order of one‐half of what can be easily realized with a gasoline engine–powered vehicle.
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