Jun 05, 20 otto cycle any piston, four stroke engine will depend on numerous factors compression ratio, explosion ratio, isentropic expansion ratio. 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. Fuel is sprayed into the cylinder at high pressure when the compression is complete, and there is ignition without a spark. Apply first law closed system to process 23, v constant. Both these processes are reversible and therefore it is the most efficient. Differences between diesel cycle and otto cycle engineering. It was a lowrpm machine, and only fired every other stroke due to the otto cycle, also designed by otto. So, there is a difference between otto and diesel cycle when we consider their processing.
It consist of four processes, two isentropic reversible adiabatic processes and two isochoric constant volume processes. If is too high, the mixture will ignite without a spark at the wrong location in the cycle. Jul 29, 2019 carnot cycle pdf explanation and derivation of carnot cycle. Efficiency of an otto engine under alternative power optimizations. Nov 21, 2017 otto cycle vs diesel cycle vs duel cycle comparison between otto cycle, diesel cycle and duel cycle comparison of ts diagram of all three cycles comparison when compression ratio is same. It has comparatively has higher thermal efficiency. Comparing carnot, stirling, otto, brayton and diesel cycles. Difference between otto cycle and diesel cycle mechanical. Otto cycle uses the spark plugs to light the charge, which is a mixture of air and fuel.
Why is diesel cycle more thermally efficient than otto cycle. The idea of otto cycle was first unveiled by nicolas otto back then in 1876. An idealized diesel engine cycle is shown in figure 3. The otto cycle is more commonly used in modest size engines single cylinders for lawn mowers, etc. Except for specific cases, in the course of the suction, the pressure is lower than the atmospheric pressure, while. A first course on thermodynamics may teach the efficiency of the otto cycle which is the ideal cycle used to simulate the gasoline spark ignition auto engine. Otto cycle the maximum efficiency of an ideal otto cycle engine, is given by 1. The ideal otto cycle efficiency is shown as a function of the compression ratio in figure 3. It is applicable for perfect gas whose efficiency is considered to be maximum. Otto cycle efficiency is given by efficiency increases with increase in compression ratio and specific heat ratio. Carnot cycle carnot cycle is theoretical thermodynamic cycle. Both these cycle are air standard cycles of automobile engines. Otto cycle is not a carnot cycle, so there is no reason carnot efficiency should apply to otto cycle. The working of a petrol engine can be approximated to an otto cycle with a.
Expression for efficiency of otto cycle gas power cycles thermodynamics. It is the thermody namic cycle most commonly found in automobile engin es. Thermal efficiency for otto cycle in general the thermal efficiency. 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. Physics stack exchange is a question and answer site for active researchers, academics and students of physics. Ottos engine work during the eve of the industrial revolution was a critical development leading to the dawn of the automotive industry in. Otto cycle that are thermal efficiency of the otto cycle, thermal efficiency of the otto cycle is equal to 1 upon 1 upon r c to the power k right. In otto cycle as well as in diesel cycle heat rejection takes place at constant volume. Expression for efficiency of otto cycle video lecture of gas power cycles chapter from thermodynamics subject for mechanical engineering students. Comparison of brayton cycle with otto cycle me mechanical.
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. Theoretical study of combustion efficiency in an otto engine. What are carnot cycle, otto cycle, and diesel cycle. The entire modern petrol engine works on otto cycle. The compression ratio of an airstandard otto cycle is 9. This means that the ideal otto cycle cannot achieve the carnot efficiency determined by the highest and lowest temperature during the cycle. Through the combustion of fuel, heat is added in a constant volume isochoric process process, followed by an adiabatic expansion process power c stroke. 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. The effects of cycle temperature and cycle pressure ratios on the. Carnot heat engine is a theoretical construct and carnot be built in practice. An otto cycle with a volume compression ratio of 9 is required to produce a net work output of 450 kj cycle. The temperature at the end of the isentropic expansion process is 800 k.
The otto cycle or the constant volume cycle is employed for petrol and gas engines, in which combustible mixture is drawn in the engine cylinder during suction stroke or induction stroke. 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. An otto cyc le is an idealized thermodyna mic cy cle that describes the functioning of a typical spark ignition piston engine. Carnot cycle pdfexplanation,derivation of carnot cycle with. Assume the working fluid is an ideal gas, and the volume effect of moles of gas generated is small relative to the effect of heating. Expression for efficiency of otto cycle gas power cycles. Otto cycle works on four processes, which commences with intake stroke where the mass of air is pushed into the piston at unvarying pressure. Efficiency of otto cycle file exchange matlab central. Such a course would derive the following equation for the otto cycle efficiency. This type of spark ignition engines is the most common type of engines used in automobiles. The airstandard otto cycle thermal efficiency is a function of compression ratio and a typical gasoline automotive engine operates at around 25% to 30% of thermal efficiency. Performance of an otto engine with volumetric efficiency journal of. Pdf effects of combustion efficiency on an otto cycle researchgate.
In the otto cycle, heat addition takes place at constant volume. It is the thermodynamic cycle most commonly found in automobile engines. The ideal otto cycle achieves the carnot efficiency of an engine working between the maximum, precombustion, temperature and the intake temperature. These processes can be easily understood if we understand pv pressurevolume and ts temperatureentropy. An otto cycle is an idealized thermodynamic cycle that describes the functioning of a typical spark ignition piston engine. It represents the ideal cycle for a spark ignition engine. The main difference between otto cycle and diesel cycle is that in otto cycle heat addition takes place at constant volume and in diesel cycle heat addition. Otto cycle otto engine in 1876, a german engineer, nikolaus august otto advanced the study of heat engines by building of the first working fourstroke engine. Spark ignition engine is a type of internal combustion engines below are pv and ts diagrams of the otto cycle. Otto cycle calculationotto cycle calculation problem statement. Otto cycle efficiency derivation mechanical engineering. Hindi otto cycle vs diesel cycle vs duel cycle comparison. 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. How can the otto cycle be improved to increase efficiency.
The design of an engine will try to achieve the maximum power, fuel efficiency, speed etc. The effect of the volumetric efficiency on the irreversible cycle. Pdf this paper explains how the combustion efficiency influence the performance of an irreversible otto cycle under conditions of varying. The real cycle of the otto engine presents, finally, another important difference when compared with the theoretical otto cycle. The otto engine was a large stationary singlecylinder internal combustion fourstroke engine designed by the german nikolaus otto. Difference between otto cycle and diesel cycle with pdf. Suction stroke during suction stroke, the piston is moved downward by the crankshaft, which is revolved either by the momentum of the flywheel or by the power generated by the electric starting motor. Efficiency is the proportion of the work and the supplied heat. Pdf effects of combustion efficiency on an otto cycle. We find that in the correlated fluctuations case, the power output and the efficiency of both cycles reach bigger fluctuations than in the uncorrelated cases. Department of energy defining pathways to maximize engine efficiency for future goal setting goals.
At the end of the articles, you will find the pdf which you can easily download. Apr 11, 2018 so, the otto cycle is more suitable for the reciprocating type of field. It means that otto cycle gives more work than diesel cycle for same compression ratio. 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. The carnot cycle consists of two isothermal processes and two adiabatic processes. Efficiency of an otto engine under alternative power. Otto cycle is one type of air standard cycle which is designated as the ideal cycle for the operation of internal combustion spark ignition reciprocating engines. As the compression ratio, increases, increases, but so does.
Otto and diesel engine models with cyclic variability scielo. It is a gas power cycle that is used in spark ignition engine i. Since process 12 is isentropic, t t v v t t v vr k k k 2 1 1 2 1 1 2 2 1 1 1 1 f hg i kj f hg i kj f hg i kj. Otto cycle is used for petrol or spark ignition engine while diesel cycle is used for diesel or compression ignition engine. Wilhelm maybach 18461929, one of the most important german engineers, perfected the construction, which was produced in large quantities already at the. Today we will attempt to study it and understand what comprises of this otto cycle. Derivation of airstandard efficiency of otto cycle. In essence the otto cycle efficiency is considerably less than the carnot efficiency, between the same temperature limits, since the heat transfer processes in the otto cycle are not reversible.
O tto cycle is a gas power cycle that is used in sparkignition internal combustion engines modern petrol engines. The current studys value is generally educational, and may also serve as guidance for engineers performing detailed simulations or conducting expensive experiments in the field. The idealized diagrams of a fourstroke otto cycle both diagrams. Power cycles otto,diesel, carnot,brayton,dual cycle. For purposes of illustration, we will assume that we want to design an otto cycle that takes 1kg of air at ambient conditions of 15c and 100kpa, compresses it to oneeighth its original volume and adds 1800kj of heat to it in its combustion process. The overall performance and efficiency of the ottocycle. On both pv and ts diagrams, the area enclosed by the process curve represents the net work of the cycle. Otto cycle and diesel cycle with diagram ic engine. Investigate the practical and thermodynamic efficiency limits of ic engines. Why is diesel cycle more thermally efficient than otto. Airstandard efficiency thermal efficiency of otto cycle, from my previous article, if you have any ideas or suggestions about airstandard efficiency of otto cycle, you can comment on this article. In a fourstroke ottocycle sparkignition engine, the four strokes are as follows.
Otto cycle is a gas power cycle that is used in sparkignition internal combustion engines modern petrol engines. The charge is drawn in by the cylinders during the intake stroke. Maximizing the efficient power gives a compromise between power and efficiency. At the time of heat addition, the piston is at the top dead centre tdc. At same compression ratio at same compression ratio diesel cycle efficiency is less than otto cycle. From the expression for efficiency of otto cycle we observe that as the compression ratio is increased, the thermal efficiency increases. Before understanding the method for determination of the efficiency of the otto cycle, we will have to remind here various processes involved. 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. So, this is very important that thermal efficiency of the otto cycle is basically 1 upon 1 1 by r c to the power k minus 1, k minus 1, not k.
The efficiency of otto cycle is less as compared with the diesel cycle. Otto cycle plotting and thermal efficiency using matlab. In order to express the efficiency of the otto cycle, we need to evaluate the work performed by the gas during one cycle and the heat which the gas received during this cycle. Nov 11, 20 for the love of physics walter lewin may 16, 2011 duration. Ans 46% an engine working on otto cycle has efficiency of 50% and index of adiabatic compression is 1. In an otto cycle the temperature at the beginning and end of compression are and. An internal combustion engine is exposed to the highest temperature after combustion of fuel only for a short duration, and it gets time to become cool in the other processes of the thermodynamic cycle. 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. When the efficiency of diesel cycle approaches the otto. Otto cycle the thermal efficiency of the otto cycle depends only on compression ratio and specific heat ratio as expected the indicated mean effective pressure imep depends on heat addition and compression ratio 34.
Pdf probably the most well established and modelled compression and expansion process in. Today we will be studying the differences between otto and diesel cycle is very detail. Aug 06, 2015 the otto cycle has less compression ratio 7. Any modification that increases the ratio of these two areas will also increase the thermal efficiency of the cycle. Petrol engines work on principle of otto cycle whereby to supply the fuel into the combustion chamber carburator is used. Effects of combustion efficiency on an otto cycle article pdf available in international journal of exergy 72 january 2010 with 2,670 reads how we measure reads. In 1876, a german engineer, nikolaus august otto advanced the study of heat engines by building of the first working fourstroke engine. Otto cycle efficiency collection of solved problems. Otto cycle is the theoretical thermodynamic cycle which describes the working of a spark ignition engine. The otto cycle is the ideal cycle for a pistondriven gasoline engine. Chapter 9 gas power cycles universiti tenaga nasional. If the compression ratio of an otto cycle and a diesel cycle. The myth of the highefficiency externalcombustion stirling.
In an ideal spark ignition engine, there are four processes as follows. For a cyclic process, the change in the total internal energy of the gas during one cycle is zero. Jan 25, 2015 this is an interesting question, particularly because the definition of better is undefined. The power density criterion is defined as the power per minimum specific volume in the cycle and the efficient power criterion is defined as multiplication of the power by the efficiency of the otto cycle. It is defined as the ratio between work done during otto cycle to the heat supplied during otto cycle. We can make all sorts of arguments about thermal efficiency, and related engineering concepts, but the interesting thing is this. The main difference between otto and diesel cycle is that the otto cycle has low thermal efficiency and the diesel cycle has high thermal efficiency. A system undergoing carnot cycle is called carnot heat engine. So the thermal efficiency in this idealised cycle is dependent only on the.
Otto cycle is a thermodynamic cycle upon which a spark ignition engine works. The thermal efficiency of the ideal otto cycle increases with an increasing compression ratio. Difference between real and theoretical otto cycles. Otto cycle any piston, four stroke engine will depend on numerous factors compression ratio, explosion ratio, isentropic expansion ratio. Otto cycle engine an overview sciencedirect topics. Mar 04, 2018 what are the four processes of diesel cycle. Calculate the mass of air to be used if the maximum and minimum temperatures in the cycle are 0oc and 20oc respectively. Comparison between otto, diesel and dual cycle 1 4 v s 1 4 for the same compression ratio and same heat input 1234 otto cycle, 1234 diesel cycle and. The diesel cycle efficiency depends upon the cutoff ratio.
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