ME152L - Experiment 5 - Amahmud PDF

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Warning: TT: undefined function: 32 MAPÚA UNIVERSITY Muralla St. Intramuros, Manila School of Mechanical and Manufacturing EngineeringEXPERIMENT NO. 5DIESEL ENGINE09 MAHMUD, Ali R. Date of Performance: January 10, 20192015151413 Date of Submission: January 16, 2019ME1 52 L – E0 1Group No. 1Engr. Teo...

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MAPÚA UNIVERSITY Muralla St. Intramuros, Manila School of Mechanical and Manufacturing Engineering

EXPERIMENT NO. 5 DIESEL ENGINE

09 MAHMUD, Ali R. 2015151413 ME152L – E01 Group No. 1

Date of Performance: January 10, 2019 Date of Submission: January 16, 2019

GRADE Engr. Teodulo A. Valle Instructor

TABLE OF CONTENTS

Objectives Theory and Principle List Of Apparatus Procedure Set-up of Apparatus Computations Discussion of Result Questions and Answers Conclusion Reference Preliminary Data Sheet

Page 1 Page 1 Page 11 Page 12 Page 13 Page 14 Page 17 Page 18 Page 20 Page 21 Page 22

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OBJECTIVES 1. To familiarize ourselves with the engine operation. 2. To be able to know the basic principle behind the operation. 3. To determine and understand the different parts and functions. 4. To be able to calculate the different parameters of our M.E. laboratory engine when subjected to varying loads. THEORY AND PRINCIPLE Diesel engine, any internal-combustion engine in which air is compressed to a sufficiently high temperature to ignite diesel fuel injected into the cylinder, where combustion and expansion actuate a piston. It converts the chemical energy stored in the fuel into mechanical energy, which can be used to power freight trucks, large tractors, locomotives, and marine vessels. A limited number of automobiles also are diesel-powered, as are some electric-power generator sets. The diesel engine is an intermittent-combustion piston-cylinder device. It operates on either a two-stroke or four-stroke cycle (see figure); however, unlike the spark-ignition gasoline engine, the diesel engine induces only air into the combustion chamber on its intake stroke. Diesel engines are typically constructed with compression ratios in the range 14:1 to 22:1. Both twostroke and four-stroke engine designs can be found among engines with bores (cylinder diameters) less than 600 mm (24 inches). Engines with bores of greater than 600 mm are almost exclusively two-stroke cycle systems. The diesel engine gains its energy by burning fuel injected or sprayed into the compressed, hot air charge within the cylinder. The air must be heated to a temperature greater than the temperature at which the injected fuel can ignite. Fuel sprayed into air that has a temperature higher than the “auto-ignition” temperature of the fuel spontaneously reacts with the oxygen in the air and burns. Air temperatures are typically in excess of 526 °C (979 °F); however, at engine startup, supplemental heating of the cylinders is sometimes employed, since the temperature of the air within the cylinders is determined by both the engine’s compression ratio and its current operating temperature. Diesel engines are sometimes called compression-ignition engines because initiation of combustion relies on air heated by compression rather than on an electric spark. 1

Fig.1. Typical sequence of cycle in a diesel engine In a diesel engine, fuel is introduced as the piston approaches the top dead center of its stroke. The fuel is introduced under high pressure either into a pre-combustion chamber or directly into the piston-cylinder combustion chamber. With the exception of small, high-speed systems, diesel engines use direct injection. Diesel engine fuel-injection systems are typically designed to provide injection pressures in the range of 7 to 70 MPa (1,000 to 10,000 pounds per square inch). There are, however, a few higher-pressure systems. Precise control of fuel injection is critical to the performance of a diesel engine. Since the entire combustion process is controlled by fuel injection, injection must begin at the correct piston position (i.e., crank angle). At first the fuel is burned in a nearly constant-volume process while the piston is near top dead center. As the piston moves away from this position, fuel injection is continued, and the combustion process then appears as a nearly constant-pressure process. The combustion process in a diesel engine is heterogeneous—that is, the fuel and air are not premixed prior to initiation of combustion. Consequently, rapid vaporization and mixing of fuel in air is very important to thorough burning of the injected fuel. This places much emphasis on injector nozzle design, especially in direct-injection engines. 2

Engine work is obtained during the power stroke. The power stroke includes both the constant-pressure process during combustion and the expansion of the hot products of combustion after fuel injection ceases. Diesel engines are often turbocharged and aftercooled. Addition of a turbocharger and aftercooler can enhance the performance of a diesel engine in terms of both power and efficiency. The most outstanding feature of the diesel engine is its efficiency. By compressing air rather than using an air-fuel mixture, the diesel engine is not limited by the pre-ignition problems that plague high-compression spark-ignition engines. Thus, higher compression ratios can be achieved with diesel engines than with the spark-ignition variety; commensurately, higher theoretical cycle efficiencies, when compared with the latter, can often be realized. It should be noted that for a given compression ratio the theoretical efficiency of the spark-ignition engine is greater than that of the compression-ignition engine; however, in practice it is possible to operate compression-ignition engines at compression ratios high enough to produce efficiencies greater than those attainable with spark-ignition systems. Furthermore, diesel engines do not rely on throttling the intake mixture to control power. As such, the idling and reduced-power efficiency of the diesel is far superior to that of the spark-ignition engine. The principal drawback of diesel engines is their emission of air pollutants. These engines typically

discharge

high

levels

of

particulate

matter

(soot),

reactive

nitrogen compounds (commonly designated NOx), and odor compared with spark-ignition engines. Consequently, in the small-engine category, consumer acceptance is low. A diesel engine is started by driving it from some external power source until conditions have been established under which the engine can run by its own power. The simplest starting method is to admit air from a high-pressure source about 1.7 to nearly 2.4 MPa to each of the cylinders in turn on their normal firing stroke. The compressed air becomes heated sufficiently to ignite the fuel. Other starting methods involve auxiliary equipment and include admitting blasts of compressed air to an air-activated motor geared to rotate a large engine’s flywheel; supplying electric current to an electric starting motor, similarly geared to the engine flywheel; and applying a small gasoline engine geared to the engine flywheel. The selection of the most suitable starting method depends on the physical size of the engine to be started, the nature of the connected load, and whether or not the load can be disconnected during starting. 3

Gasoline engines and diesel engines both work by internal combustion, but in slightly different ways. In a gasoline engine, fuel and air is injected into small metal cylinders. A piston compresses (squeezes) the mixture, making it explosive, and a small electric spark from a sparking plug sets fire to it. That makes the mixture explode, generating power that pushes the piston down the cylinder and (through the crankshaft and gears) turns the wheels. You can read more about this and watch a simple animation of how it works in our article on car engines. Diesel engines are similar, but simpler. First, air is allowed into the cylinder and the piston compresses it—but much more than in a gasoline engine. In a gasoline engine, the fuel-air mixture is compressed to about a tenth of its original volume. But in a diesel engine, the air is compressed by anything from 14 to 25 times. If you've ever pumped up a bicycle tire, you'll have felt the pump getting hotter in your hands the longer you used it. That's because compressing a gas generates heat. Imagine, then, how much heat is generated by forcing air into 14-25 times less space than it normally takes up. So much heat, as it happens, that the air gets really hot—usually at least 500°C (1000°F) and sometimes very much hotter. Once the air is compressed, a mist of fuel is sprayed into the cylinder typically (in a modern engine) by an electronic fuel-injection system, which works a bit like a sophisticated aerosol can. (The amount of fuel injected varies, depending on how much power the driver wants the engine to produce.) The air is so hot that the fuel instantly ignites and explodes without any need for a spark plug. This controlled explosion makes the piston push back out of the cylinder, producing the power that drives the vehicle or machine in which the engine is mounted. When the piston goes back into the cylinder, the exhaust gases are pushed out through an exhaust valve and, the process repeats itself. In theory, spark-plug gasoline engines should be more efficient than diesel engines. In practice, the reverse is true: diesel engines are up to twice as efficient as gasoline engines—around 40 percent efficient that is. In simple terms, that means you can go much further on the same amount of fuel (or get more miles for your money). There are several reasons for this. First, the lack of a sparking-plug ignition system makes for a simpler design that can easily compress the fuel much more—and compressing the fuel more makes it burn more completely with the air in the cylinder, releasing more energy. There's another efficiency saving too. In a gasoline engine that's not working at full power, you need to supply more fuel (or less air) to the cylinder to keep it working; diesel engines don't have that problem so they need less fuel when they're working at 4

lower power. Another important factor is that diesel fuel carries slightly more energy per gallon than gasoline because the molecules it's made from have more energy locking their atoms together (in other words, diesel has a higher energy density than gasoline). Diesel is also a better lubricant than gasoline so a diesel engine will naturally run with less friction. Diesel and gasoline are quite different. Essentially, diesel is a lower-grade, less-refined product of petroleum made from heavier hydrocarbons (molecules built from more carbon and hydrogen atoms). Crude diesel engines that lack sophisticated fuel injection systems can, in theory, run on almost any hydrocarbon fuel—hence the popularity of biodiesel (a type of biofuel made from, among other things, waste vegetable oil). The inventor of the diesel engine, Rudolf Diesel, successfully ran his early engines on peanut oil and thought his engine would do people a favor by freeing them from a dependency on fuels like coal and gasoline. Diesels are the most versatile fuel-burning engines in common use today, found in everything from trains and cranes to bulldozers and submarines. Compared to gasoline engines, they're simpler, more efficient, and more economical. They're also safer, because diesel fuel is less volatile and its vapor less explosive than gasoline. Unlike gasoline engines, they're particularly good for moving large loads at low speeds, so they're ideal for use in freight-hauling ships, trucks, buses, and locomotives. Higher compression means the parts of a diesel engine have to withstand far greater stresses and strains than those in a gasoline engine. That's why diesel engines need to be stronger and heavier and why, for a long time, they were used only to power large vehicles and machines. While this may seem a drawback, it means diesel engines are typically more robust and last a lot longer than gasoline engines. Pollution is one of the biggest drawbacks of diesel engines: they're noisy and they produce a lot of unburned soot particles, which are dirty and hazardous to health. In theory, diesels are more efficient, so they should use less fuel, produce fewer carbon dioxide emissions, and contribute less to global warming. In practice, there's some argument over whether that's really true. Some laboratory experiments have shown average diesel emissions are only slightly lower than those from gasoline engines, although manufacturers insist that if similar diesel and gasoline cars are compared, the diesels do indeed come out better. According to the British Society: "Diesel cars have contributed massively to reducing CO2 emissions. Since 2002, buyers choosing diesel have saved almost 3 million tonnes of CO2 from going into the atmosphere." Diesel engines do 5

tend to cost more initially than gasoline engines, though their lower running costs and longer operating life generally offsets that. Diesel cycle is an air-standard cycle (a combustion process), which is used to design mostly compression ignition engines.

Fig.2. Diesel Cycle The following processes are part of the diesel cycle: Isentropic Compression (Process 1–2) •

This process is called isentropic as there is no heat transferred (adiabatic) to or from the system and it is a reversible process.

•

The gas inside the cylinder is compressed isentropically from a volume V1 to V2.

•

The ratio of V1 and V2 is referred to as the compression ratio.

•

Work is done by the piston on gases (negative work Win), which means external work has to be done to compress the gases.

•

This process is characterized by the compression stroke of the 4-stoke cycle.

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Isobaric Heat Addition (Process 2–3) • • • • •

Isobaric means that the process carried out at constant pressure. With the pressure being constant, heat is added externally until volume V3 is reached. The ratio of V3 and V2 is referred to as the cut-off ratio. Heat is added to the system (positive heat Qin), by combusting the air-fuel mixture. This process is characterized by the initial part of the power stroke of the 4-stroke cycle, until volume has expanded to V3.

Isentropic Expansion (Process 3–4) • • • • •

This process is also isentropic. The gas inside the cylinder expands from V3 to V4 which is equal to V1. The ratio of V4 (or V1) and V3 is known as the expansion ratio. Work is done by the gases on the piston (positive work Wout), thus powering the engine by pushing the piston down. This process is characterized by the final part of the power stroke of the 4-stroke cycle, until volume has expanded to V4.

Isochoric Expansion (Process 4–1) • • • •

Isobaric means that the process carried out at constant volume. With the volume being constant, heat is removed until pressure comes down to p1. Heat is removed from the system (negative heat Qout), by flushing out the combusted gases. This process is characterized by the exhaust and intake stroke of the 4-stroke cycle.

Mass and Volume Flow Many of the calculations need the mass flow of a liquid, but the instruments read volume flow. This is because the mass flow depends on the density of the liquid, which can vary with temperature. The relationship between mass and volume of a liquid is:

So:

𝑀𝑎𝑠𝑠 = 𝐷𝑒𝑛𝑠𝑖𝑡𝑦 × 𝑉𝑜𝑙𝑢𝑚𝑒

𝑀𝑎𝑠𝑠 𝐹𝑙𝑜𝑤 (𝑖𝑛 𝑘𝑔. 𝑠 −1) = 𝐷𝑒𝑛𝑠𝑖𝑡𝑦 (𝑖𝑛 𝑘𝑔. 𝑚−3 ) ×

(𝑉𝑜𝑙𝑢𝑚𝑒 𝐹𝑙𝑜𝑤 (𝑖𝑛 𝐿. 𝑠 −1)) 1000 7

Air Consumption The Airbox includes an Orifice at its inlet. The DPT1 Instrument Module shows the difference in the pressures (Δ𝑝) and the air density (𝜌) will give you the basic air flow velocity ambient air pressure (before the orifice) and the air pressure in the Airbox (after the orifice). The

(𝑈):

𝑈=√

2Δ𝑝 𝜌

To find the mass flow (𝑚󰇗𝑎 ) the air flow velocity equation is modified to separate out the

factors of density and to include the coefficient of discharge (𝐶𝑑 ) for the orifice and the orifice diameter:

𝑚󰇗𝑎 = 𝐶𝑑

𝜋𝑑2 2𝑝𝐴 Δ𝑝 √ 4 𝑅𝑇𝐴

Fuel Consumption To find the mass fuel consumption you need the volumetric fuel flow and the fuel density: 𝑀𝑎𝑠𝑠 𝐹𝑢𝑒𝑙 𝐹𝑙𝑜𝑤 (𝑖𝑛 𝑘𝑔. 𝑠 −1) = 𝐹𝑢𝑒𝑙 𝐷𝑒𝑛𝑠𝑖𝑡𝑦 (𝑘𝑔. 𝑚−3 ) ×

𝐹𝑢𝑒𝑙 𝑉𝑜𝑙𝑢𝑚𝑒 𝐹𝑙𝑜𝑤 (𝐿. 𝑠 −1) 1000

To find the specific fuel consumption (work from the fuel you need the mass fuel consumption and the mechanical power developed (measured by the Dynamometer): 𝑆𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝐹𝑢𝑒𝑙 𝐶𝑜𝑛𝑠𝑢𝑚𝑝𝑡𝑖𝑜𝑛 = Where:

𝑀𝑎𝑠𝑠 𝐹𝑢𝑒𝑙 𝐶𝑜𝑛𝑠𝑢𝑚𝑝𝑡𝑖𝑜𝑛 × 3600 𝑀𝑒𝑐ℎ𝑎𝑛𝑖𝑐𝑎𝑙 𝑃𝑜𝑤𝑒𝑟 / 1000

Specific Fuel Consumption = kg kW.ℎ−1 Mass Fuel Consumption = kg.𝑠 −1

Mechanical Power = Watts

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Air/Fuel Ratio This is simply the ratio of the air mass flow against the fuel mass flow: 𝐴𝑖𝑟/𝐹𝑢𝑒𝑙 𝑅𝑎𝑡𝑖𝑜 = Volumetric Efficiency

𝑚󰇗 𝑎 𝑚󰇗𝑓

The four stroke engine makes two revolutions for each swept volume of air that it uses, but the two stroke engine only rotates once for each swept volume. The four stroke engine piston moves down to draw air/fuel mixture in, then moves up to compress and combust the mixture. It is then forced down again by the combustion and moves up to push out the exhaust gases. The four strokes are: •

Fresh Air/ Fuel Mixture Drawn In

•

Mixture Compressed

•

Mixture Ignited

•

Exhaust Pushed Out

The volumetric efficiency is the ratio of the measured volume of air or gas that enters the engine against the calculated volume of air or gas that enters the engine against the calculated volume of air that the engine should use. For this, you need to know the engine capacity, the amount of engine strokes and its speed: 𝐶𝑎𝑙𝑐𝑢𝑙𝑎𝑡𝑒𝑑 𝑉𝑜𝑙𝑢𝑚𝑒 =

𝐸𝑛𝑔𝑖𝑛𝑒 𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦 × 𝑁 𝑆𝑡𝑟𝑜𝑘𝑒𝑠/2 × 60

NOTE: Engine capacity is normally given in cc (cubic centimeters) or Liters. You must convert this into cubic meters for the volume calculations.

100𝑐𝑐 = 0.0001𝑚3

𝑀𝑒𝑎𝑠𝑢𝑟𝑒𝑑 𝑉𝑜𝑙𝑢𝑚𝑒 =

𝑚󰇗 𝑎𝑅𝑇𝐴 𝑃𝐴 9

𝑀𝑒𝑎𝑠𝑢𝑟𝑒𝑑 𝑉𝑜𝑙𝑢𝑚𝑒 𝑉𝑜𝑙𝑢𝑚𝑒𝑡𝑟𝑖𝑐 𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 𝜂𝑉 = 𝐶𝑎𝑙𝑐𝑢𝑙𝑎𝑡𝑒𝑑 𝑉𝑜𝑙𝑢𝑚𝑒 × 100

Fig.3. 4-Stroke Cycle Heat Energy and Enthalpy The heat energy of combustion from the fuel (in Watts) is founded by the fuel consumption by the fuel consumption and its calorific value:

𝐻𝐹 = 𝑚󰇗𝑓 𝐶𝐿 × 106

The inlet air enthalpy (in Watts) is found from the air mass flow rate and the ambient temperature: 𝐻𝐴 = 𝑚𝑎󰇗 𝐶𝑝 𝑇𝐴 × 103

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Thermal Efficiency This the ratio of the heat energy of combustion from the fuel against the useful mechanical power developed by the engine: 𝜂𝑇 =

𝑀𝑒𝑐ℎ𝑎𝑛𝑖𝑐𝑎𝑙 𝑃𝑜𝑤𝑒𝑟 × 100 𝐻𝐹

Brake Mean Effective Pressure (BMEP)

This is the average mean pressure in the cylinder that would produce the measure brake output. This pressure is calculated as the uniform pressure in the cylinder as the piston rises from the top to bottom of each power stroke. The BMEP is a useful calculation to compare engines of any size. 𝐵𝑀𝐸𝑃 = Where:

60 × 𝑃𝑜𝑤𝑒𝑟 × (𝑆𝑡𝑟𝑜𝑘𝑒𝑠/2) 0.1 × 𝑆𝑝𝑒𝑒𝑑 × 𝐸𝑛𝑔𝑖𝑛𝑒 𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦

BMEP is in bar Power = Watts

Speed = Rev.𝑚𝑖𝑛−1

Engine Capacity = Cubic Centimeters (𝑐𝑚3 ) or cc

LIST OF APPARATUS 1. Diesel Engine Test Bed 2. Engine Analyzer

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PROCEDURES 1. Prepare the diesel engine test bed and the engine analyzer. 2. Connect all the wires, tubes, and pipes from the engine analyzer to the respective parts of the engine test bed. Ensure that the connections are connected properly and there must be no presence of leakage and bubbles. 3. Before starting the engine, prime the machine first. 4. Start the engine and adjust the speed by throttling the fuel inlet until it stabilize. 5. Record the data from engine analyzer directed to the computer software. 6. Verify the experimented data by re-computing the values using the formulae in the Theory and Principle part.

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SET-UP OF APPARATUS

Fig.4. Diesel Engine Test Bed

Fig.5. Engine ...