If diesel fuel is then injected into the hot air, the mixture will ignite, releasing energy. A four stroke engine means that the piston passes . The four processes in the Diesel engine are as follows:-. In two-stroke engines, there are no suction and exhaust strokes. In this process work (Win) is done by the system to compress the air. A brief but critical comparison of the merits and limitations of the two-stroke-cycle diesel engine compared with the four-stroke power unit is made below. The piston goes up and down, but we want a shaft to rotate to drive our propeller. Small low-cost diesels are not usually turbocharged. The hot air was less dense than cold . The two-stroke engine employs small powers required in autocycles, scooters, and motorcycles. During this process both the valve (Inlet and Exhaust) are closed. In four-stroke cycle engines, both SI and CI, there are four strokes completing two rotations of the crankshaft. During suction stroke, the piston moves down from the top dead centre position. Introduction to Car Headlight: Here we are going to study through pv and ts diagram in practical. When the piston is at the top of its cylinder it is on its compression stroke. These are also referred to as Headlamps. Aluminum: Introduction, Characteristics, Different Types, Application [Notes & PDF]. The diesel engine does not have a spark plug. It was invented by Hugo Gldner in 1899. Two-stroke diesels with high pressure forced induction, particularly turbocharging, make up a large percentage of the very largest diesel engines. My aim is to provide useful and engaging content to our readers. Read also: Thermodynamic Cycle: Its Classification, Working, Terms Used in Thermodynamics and More. YM is packed with information to help you get the most from your time on the water. Fuel injection starts 5 to 10 before the top dead centre on the compression stroke and continues up to 15 to 25 after the top dead centre in working stroke, depending upon the speed of the engine. The valves are operated by a variety of mechanisms on diesel and four stroke engines. After the adiabatic compression process in which entropy remains constant and the air is compressed by the piston. Often, dual valve arrangementstwo intake The air is now cooled at constant volume from temperature T4 to a temperature T4 as shown by the graph 3-4 in the figure. A stroke refers to the full travel of the piston along the cylinder, in either direction. Now the heat is added at a constant pressure of the system. Glow engines use glow plugs. The diesel engine is one type of internal combustion engine; more specifically, it is a compression ignition engine, in which the fuel is ignited by being suddenly exposed to the high temperature and pressure of a compressed gas, rather than by a separate source of ignition, such as a spark plug, as is the case in of the gasoline engine. The four strokes required for this process are the Induction or Intake Stroke, the Compression Stroke, the Power or Combustion stroke, and the Exhaust Stroke. As the piston is pulled back out of the cylinder bore by the rotating crankshaft, the engine's exhaust valves begin to ease open. The diesel engine is an intermittent-combustion piston-cylinder device. The Exhaust Stroke The fourth and final stroke of the cycle, the Exhaust Stroke is just as important to the operation of a healthy Marine Diesel Engine as any of the other three strokes. the exhaust valve opens 30 to 50 in advance of the bottom dead centre and closes 10 to 15 after the top dead centre. "Diesel" model airplane engines have variable compression ratios. In this article, we will look at the Definition, Process, PV, and TS Diagram, Derivation, and Efficiency [Notes with PDF] of Diesel Cycle. Here P1, V1, and T1 are the corresponding Pressure, Volume, and Temperature. A diesel engine operates in the same manner as a four stroke diesel engine, but reduces the four strokes of the piston into two-stroke once up and and once down of the cylinder. ; Combustion stroke: As the piston reaches the top, fuel is injected at just the right moment and ignited, forcing the piston back down. As the compression ratio in this engine is high (10 to 20), the air is finally compressed to a pressure as high as 40 Kg/cm2 at which its temperature is as high as 100C, enough to ignite the fuel. At point 4, the fuel supply is cut-off. Larger engines are almost always turbocharged. All rights reserved, Difference Between Otto Cycle and Diesel Cycle, Francis Turbine: Definition, Construction or, Casting Process: Definition, Working Process,, VenturiMeter: Definition, Construction, Working,, Orifice Meter: Definition, Construction, Working,, Injection Molding: Definition, Construction,, link to What are the different Types of Car Headlights? The maximum efficiency of the CCGT cycles was approximately 11% higher than the two-stroke diesel engine, and the minimum efficiency value was approximately 4% higher than two-stroke diesel engine due to the low specific fuel consumption of CCGT. ; Compression stroke: The piston moves back up and compresses the air. The fourth and final stroke of the cycle, the Exhaust Stroke is just as important to the operation of a healthy Marine Diesel Engine as any of the other three strokes. Diesel Cycle is the process of the Diesel Engine. Now, this is the final process in which the piston is at the bottom dead center. The heat of the engine is then transferred to the fuel at constant pressure. Introduction to Aluminum: So what ignites the fuel and allows the engine to run? For a real engine fitted to a boat, there is no elephant and we need to get air into the engine, exhaust gases out and fuel in at the right time. Exhaust A diesel engine works on diesel cycle. Diesel Engine has the lowest Specific fuel consumption. Some 19th-century or earlier experimental engines used external flames, exposed by valves, for ignition, but this becomes less attractive with increasing compression. The diesel cycle is also known as the constant pressure cycle (pressure is constant during the heat addition process). Could you describe what happens at each stage of the 4-stroke cycle? Learn how your comment data is processed. It follows the syllabus of the RYA Diesel Engine and MCA Approved Engine Course 1. Print and digital editions are available through Magazines Direct where you can also find the latest deals. So This is how diesel cycle process takes place. 4-stroke diesel engines are utilized in most heavy-duty applications such as trucks, buses and vanes etc. This is known as compression ignition. Thank you guys thank you so much for reading this article. Learn about the basic components and the working of an four stroke automobile Diesel engine.Part 2 (Stages of Combustion)https://www.youtube.com/watch?v=HapI. Copyright 2017 RPM Diesel. One classification of internal combustion diesel engines is based on the type of the engine cyclediesel engines can operate either on (1) the two-stroke cycle or (2) the four-stroke cycle. No electricity is required, except to turn the engine over fast enough to start, which can be done by hand on a small engine. Let the engine cylinder carry m kg of air at point 1. at this point let P1 and T1 and V1 be the pressure, temperature and volume of the air. Let's discuss all the process in detail. In the first of this series, we look at the 4-stroke cycle. Will you send me a copy of 4 stroke diesel engine cycle pdf?? How it works: The diesel engine: The 4-stroke cycle. A stroke refers to the full travel of the piston along the cylinder, in either direction. Diesel cycle was introduced by Dr. Rudolph Diesel in 1897. Here in this process the fuel get expanded that means the work is being out and temperature is decreasing from point 3 to point 4. The diesel engine is used in heavy vehicles like Car, Trucks, Generator, and Buses extra. The two stroke diesel engine only has advantages in the power sector that is larger than the four stroke type. Process 1-2: Isentropic compression. During the suction process, the inlet valve is open and the exhaust valve is closed. Now substituting the values of T1, T2 and T3 in equation (iii),if(typeof ez_ad_units!='undefined'){ez_ad_units.push([[300,600],'theengineerspost_com-large-mobile-banner-2','ezslot_10',675,'0','0'])};__ez_fad_position('div-gpt-ad-theengineerspost_com-large-mobile-banner-2-0'); The efficiency of the ideal diesel cycle is lower than of otto cycle, for the same compression ratio. The piston is at TDC Top dead center. Suction Stroke - With pistons moving downwards and the opening of the inlet valve creates the suction of clean air into the cylinders. These are usually driven by a chain or cog belt as shown here. Thermodynamic Cycle: Its Classification, Working, Terms Used in Thermodynamics and More. Fuel is injected through the green component, called a fuel injector. Very simplistic, I know, but the basic diesel engine is as simple as that. The cylinder is filled with . If you have any query you can comment it down and If you like the effort do not forget to share it. These advantages also make the diesel engine ideal for use in the heavy-haul railroad and earthmoving environments. While the two stroke diesel has a combustion each revolution of crankshaft, that means the 2-stroke diesel has power twice than 4 stroke. During these four-strokes, there are five actions/events to be completed. At the end of the compression stroke, the fuel (diesel) is injected into the hot compressed air where it starts burning maintaining the pressure constant. He is also an author and editor at www.theengineerspost.com. Following are 4 stages of an ideal diesel cycle. In diesel cycle engines only air is compressed in the cylinder to aa high pressure, the temperature of this compressed air becomes sufficiently high to ignite the fuel. Diesel is injected in the cylinder at the end of compression stroke which itself ignites due to the high temperature of the compressed air. If you like this note please share it with your friends. The cycle is completed in 4 strokes. Many model airplanes use very simple "glow" and "diesel" engines. Understanding how your diesel engine works is key to knowing how to look after it, and fix it when it goes wrong. Want free PDFs directly to your inbox? till then Thank You so much we will meet in another article. A 'stroke' is a movement of the Piston from one end of the Cylinder to the other end. The efficiency of the diesel cycle is more efficient than the Otto cycle but not more than the Carnot cycle which is having 75 Percent. Diesel Suction Stroke 2. The inlet valve remains closed and the exhaust opens. The diesel cycle produces more amount of power compared with less fuel to the Otto cycle. I have been on this journey since 2016. Thus, it comprises two adiabatic processes, one constant pressure heat addition process, and one constant volume heat rejection process. So only temperature increases from T2 to T3 and pressure remains constant P2=P3. Yeah sure, I have sent you the PDF file to your inbox. In a four-stroke, diesel cycle compression ignition engine, the four strokes are as follows: Suction Stroke During suction stroke, the piston moves down from the top dead centre position. The upward movement of the piston pushes the remaining gases out through the open exhaust valve. The 4 Stroke COMBUSTION CYCLE The Diesel Engine 4 Stroke cycle consists of four distinct stages carried out whilst the engine Crank Shaft does two complete turns (or as we say, two revolutions). The exhaust valve remains closed during this stroke. So this process complete in four steps: Suction, Compression, Ignition, and Exhaust. As you can see in the diagram. A car headlight is a device used to illuminate the road ahead in vehicles and is located at the front end of the vehicle. In this process, no heat is absorbed or rejected by the air if(typeof ez_ad_units!='undefined'){ez_ad_units.push([[300,250],'theengineerspost_com-banner-1','ezslot_4',673,'0','0'])};__ez_fad_position('div-gpt-ad-theengineerspost_com-banner-1-0'); We see that the air has been brought back to its original conditions of pressure, volume and temperature, thus completing the cycle. [Notes & PDF]. 1. (adsbygoogle = window.adsbygoogle || []).push({}); Copyright 2019-22 TheMechanicalEngineering.com. There are four processes in diesel cycle (as shown in diagram) Diesel Cycle Process 1-2 It is the isentropic compression of the air which is sucked in from environment. Process 2-3: Constant pressure heat addition. The diesel engine, named after Rudolf Diesel, is an internal combustion engine in which ignition of the fuel is caused by the elevated temperature of the air in the cylinder due to the mechanical compression; thus, the diesel engine is a so-called compression-ignition engine. The compression is the second process in which the air is entered into the cylinder will be compressed along with the fuel. Process 4-1: Constant volume heat rejection. In compression ignition, air is first compressed and heated; fuel is then injected into the cylinder, causing it to self-ignite. As the bag of air is very rapidly compressed by the arrival of the elephant, the arrow with exactly the correct amount of fuel arrives and penetrates the bag of now very hot air. In this process, the piston is at the top dead center. In 4 Stroke Diesel Engine, the Thermodynamic cycle will be completed in the four strokes of the position or the two revolutions of the crankshaft. Because air capacity is an important constraint on the amount of fuel that can be burned in the diesel engine, and therefore on power, turbocharging is used extensively. It ignites and forces the piston down. The piston moves upward. Two stroke engines use more fuel. At the end of the compression process, it is having high pressure and temperate, the fuel is injected into the cylinder and thus the ignition process occurs. This is in contrast to igniting the fuel-air mixture with a spark plug as in the Otto cycle (four-stroke/petrol) engine. ins.style.display='block';ins.style.minWidth=container.attributes.ezaw.value+'px';ins.style.width='100%';ins.style.height=container.attributes.ezah.value+'px';container.appendChild(ins);(adsbygoogle=window.adsbygoogle||[]).push({});window.ezoSTPixelAdd(slotId,'stat_source_id',44);window.ezoSTPixelAdd(slotId,'adsensetype',1);var lo=new MutationObserver(window.ezaslEvent);lo.observe(document.getElementById(slotId+'-asloaded'),{attributes:true}); Theoretically, the power stroke from point 4. Four-stroke Otto-cycle Spark-Ignition Engine with [P-v and T-s Diagram], Carnot Cycle: Principle Processes, Efficiency with [P-v and T-s Diagram], Stirling Cycle: Efficiency with P-v and T-s Diagram. Go through the diagram too. The two-stroke cycle ignites the fuel to deliver a power stroke each time the piston rises and falls in the cylinder, without any need for the additional exhaust and induction strokes of the four . Most diesel engines generally use the four-stroke cycle, with some larger engines operating on the two-stroke cycle. Work done = Heat supplied Heat rejected, Cut-off ratio, if(typeof ez_ad_units!='undefined'){ez_ad_units.push([[300,250],'theengineerspost_com-large-mobile-banner-1','ezslot_7',684,'0','0'])};__ez_fad_position('div-gpt-ad-theengineerspost_com-large-mobile-banner-1-0');if(typeof ez_ad_units!='undefined'){ez_ad_units.push([[300,250],'theengineerspost_com-large-mobile-banner-1','ezslot_8',684,'0','1'])};__ez_fad_position('div-gpt-ad-theengineerspost_com-large-mobile-banner-1-0_1');.large-mobile-banner-1-multi-684{border:none!important;display:block!important;float:none!important;line-height:0;margin-bottom:7px!important;margin-left:0!important;margin-right:0!important;margin-top:7px!important;max-width:100%!important;min-height:250px;padding:0;text-align:center!important}. What are the different Types of Car Headlights? Process 1-2: Reversible Adiabatic Compression Process, Process 2-3: Constant Pressure Heat addition, Process 3-4: Reversible Adiabatic Expansion Process, Process 4-1: Constant volume Heat rejection. The fuel system is larger here but where in Otto cycle has smaller. Diesel Petrol Made from Petroleum/ Crude oil More dense and more viscose Self ignition temperature is low Made from Petroleum/ Crude oil Less dense and less viscose Self ignition temperature is high. From the PV and TS Diagram the process 1 to 4 we will list some of the important terms. A gun is a one-stroke engineone with pressures over 40 times that of an internal combustion engine. When air is compressed, the effect on the air is to increase its internal energy and thus its temperature. In this process, on heat, we absorbed or rejected by the air. That is because on a 4-stroke diesel engine, combustion appears every two revolution of crankshaft. A diesel engine has no ignition system or sparking plugs. Diesel engines may be designed as either two-stroke or four-stroke cycles. The fig shows the valve timing diagram for a four-stroke diesel cycle engine. The piston moves the top dead center to the bottom dead center. Air is sucked into the cylinder through the open inlet valve which closes at the end o f the stroke. The air is expanded adiabatically from temperature T2 to a temperature T3 as shown by the graph 2-3 in Fig. The four-stroke Diesel engine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning a crankshaft. Lets imagine an elephant jumping from a height onto a bag of cool air. once per complete 4 stroke cycle. The piston then approaches its starting position at the diesel engines TDC, opening the intake valve and allow the 4 Stroke Diesel Engine Cycle to begin again. And in adiabatic compression process (4-1), Substituting the value of T1 in equations (iv) and (v). If the air is heated to above the combustion temperature of the fuel very rapidly AND if the correct amount of fuel is injected into this hot air at the correct time, the engine will run. The heat of the compressed air ignites the fuel spontaneously. In most of car, buses, bikes, and scooters, we are using four stroke engines because of its higher millage and sufficient power (torque). Thats it. The diesel cycle produces more amount of power compared with less fuel to the Otto cycle. The ideal diesel cycle consists of two adiabatic, constant pressure and constant volume processes. Conclusion: The new edition Diesels Afloat (Fernhurst, 18.99) is available at www. Read more about thermodynamic cycles in our blog: Saif M. is a Mechanical Engineer by profession. Theoretically, the fuel is injected at the end of the compression stroke and injection continued till the point of cut-off. Notify me of follow-up comments by email. they are suction and the compression combustion, expansion, exhaust. So lets start. 2-stroke engine has the power stroke then 4-stroke engine and as such develop more horsepower. Both types depend on special fuels. As we have seen at the end of the compression process the burning of fuel takes place. Petrol Engine Diesel Engine. The four stroke diesel engine works on the Diesel cycle. The Compression Stroke occurs when the inlet valve closes and the piston compresses the air, pressurized by movements of the crankshaft and the flywheel, pushing it then into the diesel engines cylinder. For diesel motorcycles, see, Other internal combustion engines without spark plugs, https://en.wikipedia.org/w/index.php?title=Diesel_cycle&oldid=1093583911, This page was last edited on 17 June 2022, at 15:04. The amount of power that is generated in any diesel engine relies on the amount fuel burnt in the combustion event, which in turn is dependent on the amount of air drawn in by the crankshaft to increase their vessels horsepower, many marine diesel engine owners choose to install turbochargers to increase the intake of combustible material. The cylinder contains full of air which is entered through the inlet port as we studied above. In the present time four stroke engines is very popular in automobile industries. Difference Between 4-stroke Diesel Engine and 4-stroke Petrol Engine By Muhammad Shafaat (14ME30) 2. Here the heat is being rejected at a constant volume process that means the pressure is decreasing P4 to P1 but volume remains constant V1=V4. I have studied Mechanical Engineering and on this platform, I try to share the content in detail and in a good format. The is added at constant pressure instead of constant volume. Today we will learn about how four stroke petrol and diesel engine works. A subscription to Yachting Monthly magazine costs around 40% less than the cover price. The winter season demonstrated the highest efficiency because the power output depended on the air mass flow. The fuel system is larger here but where in Otto cycle has smaller. Theoretically, almost twice the power can be developed with a two-stroke engine compared with a four-stroke engine. Inlet and exhaust valves remain closed. Two stroke oil is expensive; you would burn a gallon every 1000 miles if it were in a car. These are usually called upward strokes and downward strokes. The vacuum pressure of the piston moving back up the cylinder then forces the spent mixture of air and fuel in the form of hot gases through the open exhaust valve. Years ago I wrote about the one-stroke engine, which is a proper . Download marine terms As the energy is transferred into the air, the pressure and temperature increase even further to combustible levels in preparation for the next stroke. This arrangement works a bit like cars window wipers; they go from side to side, but are driven by a motor. With his first practical engine in 1897, "Diesel proved to the world that his was the most efficient . 13. During this process inlet valve is open and exhaust valve is closed. The four-stroke Diesel engine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning a crankshaft. Due to this partial vacuum, the air is sucked in at the end of the stroke the . In it, fuel is ignited by heat generated during the compression of air in the combustion chamber, into which fuel is then injected. If you have any questions about Diesel Cycle you can ask in the comment section below. 2-stroke Diesel engine; 1) Two-Stroke Diesel Engine. The cylinder having charges which are released to the engine through the exhaust port. These are respectively the suction or charging, compression, power/work or expansion, and exhaust strokes. Inlet valve opens 10 to 25 in advance of the top dead centre and closes 25 to 50 after the bottom dead centre. 0-1: Suction process (Suction stroke) 1-2: Isentropic compression process (compression stroke) 2-3: Constant volume heat addition . Diesel fuel ignites at a temperature of around 320 Celsius. The diesel cycle efficiency increases with decreases in cut-off and approaches maximum (equal to otto cycle efficiency) than cut-off is zero, i.e, p=1. A stroke refers to the full travel of the piston along with the cylinder in either direction. I have done a Diploma and Engineering degree in Mechanical and writes content since 2016. There are only two remaining strokes the compression stroke and power stroke. The exhaust valve remains closed during this stroke. During this stroke, the diesel engines intake valve must be open this allows the piston to create and pressurized vacuum with its downward motion, pulling the combustible mixture of air and fuel into the cylinder for igniting. Four-stroke engines Like a gasoline engine, a diesel engine usually operates by repeating a cycle of four stages or strokes, during which the piston moves up and down twice (the crankshaft rotates twice in other words) during the cycle. Diesel Cycle is used in two-stroke and four-stroke diesel engine. The diesel engine is accessible in both four-stroke or two-stroke designs. Entropy remians constant. For heat addition diesel is used as fuel which burns and adds heat. A 2-stroke diesel engine works on the base of the diesel cycle. This engine uses heavy fuel oil, which contains more energy and requires less refining to produce. Amrit Kumar is a Mechanical Engineer and founder of Themechanicalengineering.com. We know for constant pressure heating process (1-2), Similarly, in adiabatic compression process (2-3). Two stroke engines do not last as long as four stroke engines; there is no lubrication system in a two stroke engine so parts wear out a lot faster. Two-Stroke Diesel . How it works: The diesel engine: The 4-stroke cycle. Four-stroke diesel engines are by far the most common. A stroke refers to the full travel of the piston along with the cylinder in either direction. Aluminum is a silvery-gray metal, one of the most widespread metals on earth which makes up to 8 more than % of the Earth's core mass. The diesel cycle efficiency can be calculated from the formulas which are, (Net Work)/(Heat supplied). The air is compressed adiabatically from temperature T4 to a temperature T1 represented by the graph 4-1 in Fig. Diesel Engine has the lowest Specific fuel consumption. The important variable characterizing operational conditions in each engine is the brake mean effective pressure (b MEP), which is the mean effective pressure calculated from . Process 3-4: Isentropic expansion. For the compression process, the piston moves to the top dead center from the bottom dead center. Robert Martin. 2022 The Engineers Post - All Rights Reserved / Contact-, Four Stroke Diesel Cycle Engine and Its Working [Explained with P-v and T-s Diagram]. How diesel engines work Induction As the piston begins to move down the bore, the inlet valve opens and air is sucked in. Diesel engines may be designed as either two-stroke or four-stroke cycles. [Notes & PDF], link to Aluminum: Introduction, Characteristics, Different Types, Application [Notes & PDF], Centrifugal Casting: Definition, Parts, Working, Buffing and Polishing Process: Definition,, Difference Between the Closed cycle and Open cycle, Hot Working: Definition, Methods, Working Process,, Cold Working: Definition, Methods, Working, Stress and Strain: Definition, Formula, Types,, Twist Drill: Definition, Nomenclature, Type,, Abrasive Jet Machining: Definition, Construction,, Radiator: Definition, Types, Working, Advantages,, Drilling Machine: Definition, Parts, Operation,, Water Tube Boiler: Definition, Types, Advantages,, Lancashire Boiler: Definition, Parts, Working, Electronic Ignition System: Definition, Parts,, Slotter Machine: Definition, Types, Parts,, Difference between Otto Cycle and Diesel Cycle. The piston rises to compress air. Diesel Cycle is defined as a combustion process in which the burning of diesel fuel takes place and charge receives from the burning of diesel fuel. So Lets start with the definition first. The Cams rotate once every two turns of the Crank Shaft, i.e. The two-stroke petrol engine is simple in design than a 2-stroke diesel engine but complex in an aerodynamic and thermodynamic process. Then subscribe to our newsletter. The diesel engine is used in heavy vehicles like Car, Trucks, Generator, and Buses extra. As the engine reciprocates, the piston moves up and down the cylinder twice, with the crankshaft revolving twice. A historical implication of this is that the diesel engine could have been invented without the aid of electricity. It takes two strokes to complete a power cycle: one stroke down, one stroke up, resulting in one turn of the crankshaft. The piston moves upwards from the bottom dead centre position. Theres only one inevitable outcome: the elephant gets a free ride! Diesel cycle differs from otto cycle in one respect. Check out our engine power plant products here. It is the third process after suction and compression. Diesel fuel ignites at a temperature of around 320 Celsius. Diesel cycle engines use heavy oil, diesel oil is the most common. Enter your email address to subscribe to this blog and receive notifications of new posts by email. Promotional feature in association with GJW Direct. In practice, the ignition starts before the end of the compression stroke. See the development of the hot bulb engine and indirect injection for historical significance. The pressurized fuel is atomized within the cylinder into miniscule droplets that quickly heat up to burning temperatures as the piston makes its pass over the engine interiors TDC, or top dead center, and the mixture of fuel and air ignites, forcing the piston back down into the cylinder bore and causing the crankshaft to turn once again. So it released chemical energy and that energy push the piston to the bottom dead center. h (0.16kg/kWh) for very large marine engines (combined cycle power plants are more efficient, but employ two engines rather than one). It is the 13th element on the About me, My name is Amrit Kumar. When air is entered the piston moves TDC to BDC Bottom dead center. The P2, V2, and T2 are corresponding Pressure, Volume, and Temperature after the compression process. fernhurstbooks.com. 1. This is the stroke represents the beginning of the Four Stroke Diesel Engine, and the one in which the actual combustion event occurs in the diesel engine. The hot gases now expand adiabatically to point 5 in the cylinder pushing the piston down. So here we find out the efficiency of diesel engine.