Otto-cycle

Figure 2.2 The indicator diagrams for the Carnot and the Otto engines. The Carnot cycle operates between the two temperatures Tj and T2 only, whereas the Otto cycle undergoes a temperature increase as a result of combustion.

It follows that the efficiency of the Carnot engine is entirely determined by the temperatures of the two isothermal processes. The Otto cycle, being a real process, does not have ideal isothermal or adiabatic expansion and contraction of the gas phase due to the finite thermal losses of the combustion chamber and resistance to the movement of the piston, and because the product gases are not at tlrermodynamic equilibrium. Furthermore the heat of combustion is mainly evolved during a short time, after the gas has been compressed by the piston. This gives rise to an additional increase in temperature which is not accompanied by a large change in volume due to the constraint applied by tire piston. The efficiency, QE, expressed as a function of the compression ratio (r) can only be assumed therefore to be an approximation to the ideal gas Carnot cycle. 

Otto cycle Gasoline HC, CO, CO2, NO, Auto, truck, bus, aircraft, marine, motorcycle, tractor... 

Both gasoline and diesel engines are available in either a two-stroke- or a four-stroke-cycle design. The fundamental difference between the Otto engine cycle (named after Nikolaus Otto, who developed it in 1876) and the diesel engine cycle involves the conditions of the combustion. In the Otto cycle. 

Pressure-volume diagram for ideal Otto cycle (1-2-3-4-5), with exhaust and intake of four-stroke cycle (5-6-7) added. ... 

Toward the end of the nineteenth centuiy, successful two-stroke engines operating on the Otto cycle were developed by Dugald Clerk, James Robson, Karl Benz, and James Day. In this engine, the intake, combustion, expansion, and exhaust events all occur with but two piston strokes, or one crankshaft revolution. In principle this should double the output of a four-stroke engine of equal piston displacement. However, instead of the intake and exhaust events taking place during sequential strokes of the piston, they occur concurrently while the piston is near BDC. This impairs the ability of the... 

According to r] = l-Rf the efficiency of the ideal Otto cycle increases indefinitely with increasing compression ratio. Actual engine experiments, which inherently include the real effects of incomplete combustion, heat loss, and finite combustion time neglected in fuel-air cycle analysis, indicate an efficiency that IS less than that given by r =l-R when a = 0.28. Furthermore, measured experimental efficiency reached a maximum at a compression ratio of about 17 in large-displacement automotive cylinders but at a somewhat lower compression ratio in smaller cylinders. 

Spark-ignition, or otto cycle, engine which is fueled by a gas and air mixture,... 

The thermodynamic cycle for hydrogen is much closer to the ideal Otto cycle than for either a gasoline or a diesel engine. In addition, the compression ratio can be higher. 

A four-stroke internal combustion engine was built by a German engineer, Nicholas Otto, in 1876. The cycle patterned after his design is called the Otto cycle. It is the most widely used internal combustion heat engine in automobiles. 

The thermodynamic analysis of an actual Otto cycle is complicated. To simplify the analysis, we consider an ideal Otto cycle composed entirely of internally reversible processes. In the Otto cycle analysis, a closed piston-cylinder assembly is used as a control mass system. 

The p-v and T-s process diagrams for the ideal Otto cycle are illustrated in Fig. 3.2. 

This expression for the thermal efficiency of an ideal Otto cycle can be simplified if air is assumed to be the working fluid with constant specific heat. Equation (3.10) is reduced to... 

An engine operates on the Otto cycle and has a compression ratio of 8. Fresh air enters the engine at 27°C and 100 kPa. The amount of heat addition is 700kJ/kg. The amount of air mass in the cylinder is 0.01kg. Determine the pressure and temperature at the end of the combustion, the pressure and temperature at the end of the expansion, MEP, efficiency, and work output per kilogram of air. Show the cycle on a T s diagram. Plot the sensitivity diagram of cycle efficiency versus compression ratio. 

Take a compression device, a combustion chamber, an expander, and a cooler from the closed-system inventory shop and connect the four devices to form the Otto cycle as shown in Fig. 3.2. 

The compression ratio in an Otto cycle is 8. If the air before compression (state 1) is at 60°F and 14.7 psia, and 800Btu/lbm is added to the cycle and the mass of air contained in the cylinder is 0.025 Ibm, calculate (1) temperature and pressure at each point of the cycle, (2) the heat that must be removed, (3) the thermal efficiency, and (4) the MEP of the cycle. To solve this problem by CyclePad, we take the following steps ... 

The power output of the Otto cycle can be increased by turbocharging the air before it enters the cylinder in the Otto engine. Since the inlet air density is increased due to higher inlet air pressure, the mass of air in the cylinder is increased. Turbocharging raises the inlet air pressure of the engine above atmospheric and raises the power output of the engine, but it may not improve the efficiency of the cycle. A schematic... 

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