Understanding the working principle of a gasoline-powered vehicle necessitates knowledge not only concerning gasoline, but also knowledge regarding automobile's engine associated systems. Two forms of technology include conventional technology and advanced technology. The backbone of most cars today are conventional technology involves engine structure, combustion, and a combination of interlocked systems. Four main systems of a gasoline-powered include air, fuel, exhaust, and engine.
Working Principle of Gasoline-Powered Engine in Thermodynamic Viewpoint
According to Fisher (2015) findings, the air system conveys a mixture of fuel and air to the engine. The fuel system store gasoline in the automobile conveys gasoline to air intake system, and the mixed gasoline and air in the appropriate proportion for burning within the engine. The exhaust system emits combustion gasses to the atmosphere. In contemporary vehicles, a sophisticated computerized control device balances the typically inconsistent goals of high power, low emissions and good fuel economy (Landfahrer 117).
Combustion Cycle Thermodynamics
Consistent with Spalding (2012) description, a gasoline-powered vehicle engine is an inner combustion, spark-ignition engine that aid to burn fuel in sealed chambers known as cylinders. Engine power is produced by a quick expansion of gasses in the course of burning of compressed air and fuel mixture. Many vehicles are engines interchanging piston-type systems wherein several cylinders each have a piston, which slides from side to side. Power from the motion of one or multiple pistons is transmitted via an attaching rod to a crankshaft, which is filed to the drive wheels using drivetrain (Awano 64).
Numerous automobile gasoline engines work on a four-stroke cycle. Every stroke is a single motion of a piston, either down or up. Figure 1 below demonstrates the four-stroke cycle. The initial downward motion of the piston, known as the intake stroke, draws a combination of fuel and air into a combustion chamber via open intake valves (Landfahrer 159). While the piston inverses direction and starts to shift backward, the intake valves close. This upward movement of the piston is the compression stroke. The temperature and pressure of the air-fuel mixture are raised by this compression. Adjacent to the top of compression strokes, a spark plug generates a spark that in turn ignites the mixture. The mixture combusts and expands, driving the piston downward in its third motion, or power stroke. As the piston bottom dead center and starts to move back once more, exhaust valves open, starting the exhaust stroke.
The upward movement of the piston thrusts burned gasses outside the engine into an exhaust mixture and ultimately out an exhaust cylinder. For the combustion to take place in a cylinder, fuel has to be in vapor form, and to combust completely, fuel ought to have the correct mixture of air-fuel vapor. The best mixture, known as the stoichiometric mix, is a non-oxygenated gasoline is a 14.7:1 ration of air density to fuel density (Fisher 318). A combination featuring less air or more fuel is called fuel-rich whereas the ratio featuring more air and less fuel is called fuel-lean.
Figure 1: Four-Strokes of a Gasoline Interior Combustion Engine
Regulation of air-fuel ratio (A/F) is vital to an ideal emissions performance within an engine. Since discharge of carbon monoxide (C) and volatile organic complexes (VOCs) multiplies under fuel-rich operation and release of nitrogen oxides (NOX) increases during fuel-clean operation, most contemporary automobiles are assembled to sustain stoichiometric A/F (Awano 87).
Viewed in an appropriate sense, a gasoline interior combustion engine trails a thermodynamic cycle called Otto cycle. This cycle entails four processes to complete the cycle, which includes isentropic compression, constant volume heat addition, isentropic expression, and constant volume heat rejection (Landfahrer 206). The graph below shows Otto cycle.
Figure 2: Otto cycle
The Ideal Otto Cycle
The thermal efficiency of this cycle is the ratio of work recuperated from the cycle to heat power input to the cycle. For a suitable heat engine, a modest energy balance indicates that only heat energy becomes input, and this energy is output originating from the engine as either waste heat energy or mechanical work (Fisher 342). Mathematically, this can be presented as:
Qin = Wout +Qout
Where Qin represents heat energy, input Wout represents mechanical output from the engine, and Qout represents waste heat. Therefore, efficiency is given as:
If the constant volume heat capacity is constant, the efficiency may similarly be expressed as:
The result of this is that there is the highest efficiency obtainable by an internal burning engine. For a variety of compression ratios like a gasoline engine, the maximum efficiency is 40-60% (Spalding 544).
Engine Structure
An engine is separated into two different parts, a cylinder head. The top, or head, controls gas movement through the engine and similarly clamps spark plugs. Exhaust valves and intake poppet valves enable for accurately timed intake and exhaust movements. Spring-closed poppet valves may be opened and closed tremendously rapidly, a vital critical characteristic for optimum performance at high engine speed. Valve movement is regulated using a camshaft. As the camshaft oscillates, the lobes push counter to rocker arms to open the valve counter to spring pressure either by using pushrods or directly (Awano 115).
Air System
An air system sucks air into an engine and controls engine power. Pressure developed by piston movement draws air via a duct to an air filter that traps abrasives and contaminants like insects and dust. Air flow is regulated by a throttle attached to a spindle within the duct coming out of the air filter. The throttle is just a rotating disk that blocks the flow of air to the engine in the normal position. It is mounted to an accelerator which is depressed by a driver to tilt the disk and emission of air to the engine. Through the additional air, the engine may use more fuel and generate more power to maintain speed, accelerate, or maintain speed (Fisher 397).
Intake Air Pressurizing
Positive Crankcase Ventilation (PVC)
PVC is a technique used to modulate unburned VOC releases from the gasoline-powered cars. It engages recycling an engine's unexploited combustion gasses. In the process of combustion, high pressure within the chambers pushes a small amount of gas between the cylinder walls and piston rings. This blow-by-gases, a combination of air, unburned fuel, and combustion products culminate in the crankcase. If they are left to accumulate, they will form sufficient pressure to force oil outside the engine. To prevent this, the gasses vent through pipes and a flow control valve into the air intake system of the engine.
Fuel System Carburetor
A carburetor uses a venture to emit the precise fraction of fuel into the consumption airstream. A venture is a converging-diverging jet, primarily a pipe that tapers internal from both endings to a threat or a narrow section (Awano 124). As air circulates through the venture, velocity increases as it approaches the throat since the flow area reduces. As the air speeds up, the pressure reduces, creating a vacuum in it that draws fuel from the carburetor's fuel bowl via a small orifice known as jet. More jets are employed to supplement the mixture in the course of acceleration and to supply enough fuel at idle. A valve or choke plate is utilized to enrich the mix when the engine becomes cold by reducing the amount of air obtainable to the engine (Spalding 612).
Conclusion
The thermodynamic efficiency of gasoline engine was recognized to be an essential source of controversy due to the reality that efficiency surpasses that standard one. Concerning this matter, it is suggested that the second law of efficiency should be applied so as to attain consistent measurable on the gasoline engine performance.
Works cited
Awano, Seiichi. Thermodynamical Performances of Four-cycle Gasoline Engines. Tokyo: Research Institute of Technology, Nihon U, 2013. Print.
Fisher, J. B. "Fuel And Lubricant Requirements For Gasoline Compression-Ignition Oil Engines And Spark-Ignition Oil Engines." (2014). Web. 25 Mar. 2015.
Landfahrer, Klaus. Thermodynamic Evaluations and Optimization of Two-stroke Gasoline Engine. Warrendale, PA: Society of Automotive Engineers, 2011. Print.
Spalding, D. Brian. Heat and Mass Transfer within Gasoline and Diesel Engines. New York: Hemisphere, 2012. Print.
