As an automobile is driven, the equivalence ratio and intake pressure vary with the engine load. Of course, modern engine design is today fully and accurately simulated in computer software, but it still remains useful to perform long hand calculations on idealised gas models to. The otto cycle is a set of processes used by spark ignition internal combustion engines. Power bhp plan33,000 p is brake mean effective pressure, in psi l is piston stroke, in feet. According to the method of igniting the fuel a spark ignition engine, b compression ignition engine and c hot spot ignition engine 5. It is the total volume maximum volume of the cylinder in which otto cycle takes place. Otto cycle 4 stroke engines are commonly used in most cars and trucks today. Derivation of airstandard efficiency of otto cycle. Calculate the mass of air to be used if the maximum and minimum temperatures in the cycle are 0oc and 20oc respectively. Prior to the isentropic compression process, the air is at 100kpa, 35isentropic compression process, the air is at 100kpa, 35oc, and 600 cmc, and 600 cm3. In the otto cycle, heat addition takes place at constant volume. Thermodynamic cycle calculations for a pumped gaseous. In ideal otto cycles, airstandard assumption is used. The 2 in the denominator would become a 1 for a two cycle engine.
Brayton cycle reading problems 98 910 978, 984, 9108 open cycle gas turbine engines after compression, air enters a combustion chamber into which fuel is injected the resulting products of combustion expand and drive the turbine combustion products are discharged to the atmosphere compressor power requirements vary from 4080% of the power output of the turbine re. The idealised otto cycle for a spark ignited gas is shown in fig. On this page we discuss the otto thermodynamic cycle which is used in all internal combustion engines. It is the thermodynamic cycle most commonly found in automobile engines. An otto cycle is an idealized thermodynamic cycle that describes the functioning of a typical spark ignition piston engine. Solution the diesel cycle differs from the otto cycle in the heat addition process only. The following link by the kruse technology partnership presents a description. The british engineer james atkinson 18461914 realized that the efficiency of the otto cycle could be improved if the combustion gases could be expanded to near atmospheric pressure before being exhausted from the engine. I n my previous article, i gave a short introduction to otto cycle and discussed the processes in it.
The working of a petrol engine can be approximated to an otto cycle with a. In this configuration, high compression ratios can be used and rapid combustion can be achieved. How to calculate thermal efficiency of rankine cycle. The student will type numerical parameters and excel will perform the calculations. Lin and hou 16 investigated the e ects of heat loss, as characterized by a percentage of fuels energy, friction and arviable speci c heats of the working uid, on the per. Comparing carnot, stirling, otto, brayton and diesel cycles. At this speed, each stroke in the cycle takes place in 20 ms. The otto cycle is the ideal cycle for sparkignition engines, in honor of nikolaus otto, who invented it in 1867.
Em111 2011 q4 calculations for an otto cycle youtube. According to the number of strokes per cycle a four stroke and b two stroke engine 4. An idealized diesel engine cycle is shown in figure 3. Probably the most well established and modelled compression and expansion process in the power chamber of an internal combustion engine is the otto cycle. The intake air is at 100 kpa 1 bar, 20 c, and the volume of the chamber is 500 cm. The first law of thermodynamics for closed systems d the airstandard otto cycle sparkignition engine. An otto cycle of a gasoline engine, is an idealized. The entire modern petrol engine works on otto cycle. The average force on the piston throughout one cycle is f where f mep x area of piston pa the mean effective pressure p is the mean pressure during the cycle. Otto s engine work during the eve of the industrial revolution was a critical development leading to the dawn of the automotive industry in the late 19th century. The area bounded by the complete cycle path represents the total work that can be done during one cycle. This 10 pdh professional development hour course includes a series of input data and solved output equations in an excel format.
Otto cycle are always found to be higher than those for the atkinson cycle at the same operating conditions. If we use the isentropic equations with the ideal gas law, we see that t 2 t 1 p 2 p 1. Knowing the temperatures, this is an easier calculation. Therefore, equations pertaining to steadyflow systems should be used in the analysis of the rankine cycle, and equations pertaining. The free piston linear alternator illustrated in figure 2 has been designed in hopes of approaching ideal otto cycle performance through hcci operation. Calculations relating to an otto cycle, including calculating all pressures and volumes, drawing a pv diagram, calculating the work for each process and calculating the power output.
Look at different cycles that approximate real processes. These engines a ingest a mixture of fuel and air, b compress it, c cause it to react, thus effectively adding heat through converting chemical energy into thermal energy, d expand the combustion products. The temperature at the end of the isentropic expansion process is 800 k. The ideal otto cycle consists of four internal reversible processes. The otto cycle is often plotted on a pressure volume diagram pv diagram and on a temperatureentropy diagram ts diagram. It consist of four processes, two isentropic reversible adiabatic processes and two isochoric constant volume processes. Power cycles carnot, brayton, otto, diesel, magnetohydrodynamics and fuel cell calculator. In this article, i will derive the airstandard efficiency of otto cycle. From that data, the cells in the second grid are updated, and pressurevolume and temperatureentropy diagrams are generated. We can also evaluate the work w by the difference of the heat into the gas minus the heat rejected by the gas. The work done during one cycle is w f l pal l is the stroke. Thermodynamic modeling of an atkinson cycle with respect.
The pressure is near atmospheric pressure and the gas. Two other terms frequently used in conjunction with reciprocating engines are compression ratio r and mean effective pressure mep. Before calculating thermal efficiency of rankine cycle, lets understand about rankine cycle. Otto cycle the otto cycle is named after nikolaus otto 18321891, german who is credited as the first creator of a petroleum fuel based internal combustion engine operating under a four stroke cycle. At the beginning of the compression process, air is at 95. The otto cycle is a description of what happens to a mass of gas as it is subjected to changes of pressure, temperature, volume, addition of heat, and removal of heat.
At the beginning of the compression process, air is at 100 kpa and 17c, and 800 kjkg of heat is transferred to air during the constantvolume heataddition process. We can calculate the work by determining the area enclosed by the cycle on the pv diagram. The user must fill in the data in the top grid from other software or table lookup. An otto cycle is an idealized thermodynamic cycle that describes the functioning of a typical. At the time of heat addition, the piston is at the top dead centre tdc.
Carnot cycle there are only two temperatures in the carnot cycle heat is added at t h heat is rejected at t l there are four temperatures in the otto cycle heat is added over a range of temperatures heat is rejected over a range of temperatures. Fuel is sprayed into the cylinder at high pressure when the compression is complete, and there is ignition without a spark. Otto cycle calculationotto cycle calculation problem statement. Otto cycle engine an overview sciencedirect topics.
Carnot cycle pv, ts diagram pv diagram of otto cycle. Calculation example an ideal otto cycle has a compression ratio of 8. Chapter 3d the first law closed systems otto cycle. If the mass of the flywheel is sufficiently small, prominent fluctuations in the angular velocity corresponding to the power cycle will be apparent. In this example let assume an otto cycle with compression ratio of cr 9. Gas power cycles our study of gas power cycles will involve the study of those heat engines in which the working fluid remains in the gaseous state throughout the cycle. Pdf probably the most well established and modelled compression and. It has an efficiency given by 1 e oua e 1brayton r y1 2 where r is the compression ratio of the cycle andy is the ratio of the molar heat capacity at constant pressure to the molar heat capacity at constant volume. Maximum thermal efficiency of an otto cycle calculator. Accounting for the variation of specific heats of air with temperature, determine. In terms of compression ratio, the efficiency of an ideal otto cycle is. It has comparatively has higher thermal efficiency. In otto cycle engines, the pressure in the cylinder at the end of the expansion power stroke is still 3 to 5 atm when the exhaust valve opens. A free powerpoint ppt presentation displayed as a flash slide show on id.
Otto cycle efficiency collection of solved problems. In the constant volume adiabatic flame temperature case, the volume of the system is held constant hence there is no work occurring. In 1876, a german engineer, nikolaus august otto advanced the study of heat engines by building of the first working fourstroke engine. An engine working on diesel cycle has a compression ratio of 15 and cutoff takes place at 5% of the stroke. But since the processes 23 and 45 are curves, this is a difficult calculation. Wilhelm maybach 18461929, one of the most important german engineers, perfected the construction, which was produced in large quantities already at the end of the year 1876. According to the working cycle a otto cycle constant volume cycle. Using the engine stage numbering system, we begin at the lower left with stage 1 being the beginning of the intake stroke of the engine. A thermodynamic cycle comprises a series of operations carried out on the working substance ws during which heat is supplied, and after which the ws is returned to its original state for a more comprehensive introduction to thermodynamic cycles also see thermodynamic cycles an example of a thermodynamic cycle is the internal combustion engine.
Rankine cycle is a theoretical cycle in which heat energy converts into work. Otto cycle the maximum efficiency of an ideal otto cycle engine, is given by 1. The compression ratio of an airstandard otto cycle is 9. Pdf entropy generation in an overexpanded otto cycle engine. Finally, it can be shown that the cycle efficiency is e. It is a gas power cycle that is used in spark ignition engine i. We often study the ideal cycle in which internal irreversibilities and complexities the. This spreadsheet provides a template for analysis of the otto sparkignition, internal combustion cycle. Thermal efficiency compression ratio internal combustion engine expansion process high compression ratio.