Vehicle power supply and power unit (energy conversion)Vehicle Source of Energy and Power Unit Topic list:Types of vehicle power supply unitsClassification of internal combustion enginesFuel used in internal combustion enginesEngine technical specifications- oil consumptionTypes and classification of enginesThe main parts of the engine, and the engine operating systemsTypes of vehicle power supply units:Electric motor (battery powered)Combustion engine (fuel-powered)Multiple sources (hybrid cars), combustion engine + electric motor Electric motor:The electric motor works through batteries that give a constant current. This current enters a transformer to convert the DC current into alternating current. The alternating current is connected to a 3-phase alternating current electric motor. Engine:An engine is a machine that converts the energy in fuel into power and motion.Back to the list Classification of combustion engines:External combustion engine, in which fuel is burned outside the engine. As shown in the figure, the steam engine represents this type of engine. The heat generated by burning fuels is used to heat water and turn it into steam. This steam passes in tubes to reach the engine cylinders, generating pressure that drives the pistons in the engine.An internal combustion (IC) engine in which fuel is burned inside the engine. An automobile engine is an internal combustion engine as the fuel is combusted inside the engine. Other engines (rotary, turbo, etc.) are internal combustion engines.
Heat engine:Heat engines enable the conversion of heat energy into kinetic energy through the active fluid. Heat engines use a number of ways to use heat to convert pressure and a change in volume into mechanical motion. Adding energy in the form of heat to the gas will increase its temperature, but at the same time the gas law means that the gas pressure or volume or both will increase proportionally. The gas can be returned to its initial state by taking that energy back from it but not necessarily in the form of heat. A change in pressure and/or volume can be used to make work by moving a mechanical device such as a piston or a turbine blade. . The greater the temperature change, the more energy can be extracted from the active fluid.Heat engines are represented in thermodynamics using a standard thermal model called thermal cycles, Otto cycle…. etc. Motors mean the actual medium, and cycle means the theoretical model. Indicated pv diagram:The pressure and temperature graph shows the theoretical procedures that make up the cycle (constant pressure procedure, constant volume, isothermal, no heat transfer). The cycle efficiency can be calculated from the cycle graph which represents the maximum that the actual motor cannot exceed when it is running.
Actual curve for internal combustion engines (spark ignition):Most modern internal combustion engines operate on four strokes. Some other types of engines may have cycles of different strokes.
stroke:Stroke is the movement (travel) of the piston when its longitudinal movement inside the cylinder in one direction. The stroke length is determined by half a turn of the crankshaft. The stroke can also be defined as the distance traveled by the piston from the upper dead point (NPM) to the lower dead point (NPM) or vice versa. The stroke is twice the distance between the axis of the large end of the crankshaft and the axis of the crankshaft (crankshaft bend). Reciprocating piston engine:The reciprocating motion of the pistons is converted into rotational motion by the crankshaft. Four-stroke engines:
* Intake stroke: The intake valve opens. The piston moves downward, pulling the mixture of air and gasoline atomizer into the cylinder.* Compression stroke: the intake valve is closed. The piston moves up and compresses the charge.* Power stroke: The ignition system provides a spark through the spark plug that ignites the compressed charge. When the charge burns, the air heats up and expands inside the closed cylinder space, creating a high pressure that affects the surface of the piston and pushes it down.Exhaust stroke: The exhaust valve opens. The piston moves up, and pushes the exhaust gases out of the cylinder. Two-stroke engines:Two-stroke engines are similar to four-stroke car engines, but require only one turn of the crankshaft to complete the cycle.Two-stroke engines are not used in cars for the following reasons:Produces high exhaust pollutantsIt has poor power at slow speedsFour-stroke engines require more maintenanceYou need to mix oil with the fuel
Finkel motor (rotary motor)Wankel (rotary) engine : A Finkel engine, also called a rotary engine, uses a rotating triangular piston instead of a conventional piston. The rotary piston rotates in a special chamber. In one cycle during which all runs are completed.The rotary motor is a high-powered motor for its size. Since the piston rotates rather than reciprocating, it rotates smoothly and free of vibrations.The motor needs a complex pollutant control system to bring the motor to the required level of pollutant ratio
Gas turbine engine:A gas turbine engine uses burning and expansion of fuel vapor to drive a fan’s blades. The fan blades are attached to a shaft that can be used as a power output shaft. Gas turbine engine has high efficiency, much more than reciprocating engine. The engine can burn any type of fuel: gasoline, kerosene, or diesel. This type of motor can produce high power for size. Since the movement is rotational, the motor runs very smoothly. The turbocharged engine is not used in automobiles due to the high cost of its manufacture.
Back to the list Internal combustion engines fuel: Fossil fuel: It is the fuel produced from organic materials buried in the ground. And turned into fuel over a period of millions of years. The fuels are high in carbon, and they include coal and petroleum, which is divided into crude oil and natural gas. Gasoline (gas):It is a liquid with a low density, fast ignition, and rapid evaporation. Gasoline is used in spark ignition engines. Gasoline has an octane rating (number), which indicates the fuel’s resistance to knocking. The higher the octane number, the slower the combustion rate, and vice versa. The octane number specified in the specifications is in the range from 80 to 95 for passenger cars.Gasoline (Petrol) engine or spark ignition (SI), in which the fuel (gasoline) in the intake manifold is calibrated before it enters the combustion chamber and then the spark plug ignites the fuel. Diesel:It is a denser liquid than gasoline, and does not evaporate like gasoline. For this, it needs a different type of engine and a special fuel system, and it is used in trucks and trains in general, as well as in passenger cars due to the high rate of fuel saving.The calorific value of diesel is 12% higher than that of gasoline. Diesel is evaluated by the cetane number, the increase in the cetane number indicates the ability of the diesel to evaluate on the cold (ignition speed). The cetane number stated in the specification is in the range of 45.* Diesel engine or diesel engine or (compression ignition Cl), fuel (diesel) is injected into the combustion chamber of the engine directly, when fuel is injected into the cylinder, it is self-ignited. Alternative fuel:Natural gas: It is mostly methane. It is a clean alternative fuel. It is similar in properties to gasoline fuel. It can be used in the form of compressed natural gas (CNG). or a liquid form of liquefied natural gas (LNG), which is used as a fuel for cars and trucks.Dedicated natural gas vehicles that run on natural gas only.* Dual-fuel or bi-fuel vehicles that can run on gasoline or diesel in addition to natural gas.Compressed natural gas (CNG):It is similar to LPG in many respects. It is suitable for the engine and extends the service life of the engine with low maintenance cost. It is the cheapest fuel than alternative fuels (other than electricity) when comparing the energy extracted from an equal amount of fuel energy. The high octane number of natural gas allows to increase the compression ratio of the engines used for gas and thus increases the power generated compared to conventional gasoline engines.Propane – liquefied petroleum gas (LPG):It is a clean fuel that can be used to power internal combustion engines. It comes from the same sources as compressed natural gas.Biodiesel:It is extracted from vegetable oils and animal fats. It usually produces fewer pollutants than mineral-based fuels (petroleum). The mixture, consisting of a small percentage of these oils and low-level biodiesel blends, produces a fuel that can be used without problems with conventional diesel engines. Mixtures such as B2 (2% vegetable oils and 98% diesel) and B5 are now more commonly used in diesel engines due to the high characteristics of the mixture. Methanol:It is an alcoholic fuel extracted from coal, mostly from natural gas. Methanol fuel is sold as a mixture with gasoline of 85% methanol and 15% gasoline and is called M85 fuel.Ethanol:It is extracted from corn and other crops, and has lower greenhouse gas emissions than conventional fuels. Mixing a percentage of ethanol with gasoline with 85% ethanol and 15% gasoline gives the fuel called E85 fuel.* Problems associated with the use of ethanol alone, which leads to the formation of vapor in the fuel pipeline as a result of heat (vapor lock), or difficulty in cold starts, as well as the problem of not seeing the flame, led to the need to mix the standard 85% alcohol and 15% gasoline as in methanol.Hydrogen:It is the lightest gas, and makes up 75% of the mass of matter in the universe. Hydrogen is not found separately in nature, but is present in a complex form. It can be obtained by extracting it from natural gas or other types of fuel, or by using electricity to decompose water into oxygen and hydrogen. Hydrogen is used to power cars in two different ways. Hydrogen can be burned in internal combustion engines or it can be used in combination with oxygen in a fuel cell. Hydrogen is not a suitable fuel for internal combustion engines as it is more prone to the pre-ignition problem. The best and most efficient way is to use hydrogen through fuel cells.Electricity:Which can and can be obtained in many ways, by burning coal containing a high percentage of sulfur, or by power plants (engines or nuclear energy), or by methods that generate clean energy without pollution emissions (photovoltaic cells) or solar cells. , or wind energy, or energy generated from waterfalls. Electric cars are divided into battery-powered cars (charged by connection to the electricity source, which depends on electricity generated by an external source to charge batteries, plug-in vehicles, and hybrid cars that depend on a power source loaded with the car charging the batteries. The hybrid car is designed to run With any type of fuel, such as gasoline or diesel, as well as different types of alternative fuels. * Bi-fuel vehicles:It is the one in which two types of fuel are stored in two separate tanks in the car and the engine is started by using one of the two fuels alone. This is done by a manually controlled switch or by a sensor that selects the appropriate fuel for the best performance according to the operating conditions. * Flexible-fuel vehicle (FFV):It is the one that works with alternative fuels with an internal combustion engine designed to run on more than one fuel, mostly gasoline mixed with either ethanol or methanol fuel, and the two types are stored in one common tank. Flexible fuel engines are able to work with any mixture ratio formed inside the tank, as the fuel injection timing and ignition timing are self-adjusting according to the actual mixture that is recognized by electronic sensors.Back to the list Engine Technical Specifications: Engine displacement (capacity)Engine swept volume (engine displacement, engine capacity):It is the volume displaced by all the pistons inside the cylinders of an internal combustion engine during (stroke) from the upper dead point to the lower dead point. It is usually specified in cubic centimeters (cc), liters, or (particularly in North America) cubic inches displacement (CID). Engine displacement does not include the total volume of the combustion chambers. Displacement = cylinder area x stroke length x number of cylinders where:D = Cylinder bore diameter L = StrokeVe = Engine swept volume -in liters or cubic centimeters (liter, or cm3 (cc)) Engine displacement in liters or cubic centimeters Vs = Cylinder swept volume n = number of cylinders Variable displacement engine:A technology specific to automobile engines that allows engine displacement to be changed, in order to improve fuel economy, usually by deactivating the cylinders. This technique is mainly used in large multi-cylinder engines. This technology allows for increased fuel efficiency without sacrificing the maximum power of the engine. The driver can get the required traction and load when they need it, but can also get fuel economy similar to small engines, when the car is not at full load.Since at light loads the driver uses only 30% of the car’s maximum value, in this case the throttle valve is almost closed. This causes low efficiency and this phenomenon is known as pumping loss. This technology avoids these problems so that fuel consumption is reduced by 8 to 25% on highways.The work of the cylinders is neutralized by keeping the intake and exhaust valves closed. In this case, an air spring from the trapped gases inside the cylinder is formed inside the cylinders. This helps to work the required balance for the crankshaft when deactivating the cylinders without adding loads to the engine.In more modern systems, the engine control system also cuts off the injectors from the worn cylinders. It also changes the spark timing, valve timing and throttle to facilitate the engine’s operation during the transition period between idle and cylinder activation. The cylinders are mutually deflected at high speed to keep the engine balanced.There are many names for this system such as Variable Cylinder Management (VCM), Multi-Displacement System (MDS) of Chrysler, Displacement on Demand (DOD) of General Motors, Active Cylinder Control Control (ACC) for DaimlerChrysler, Modulated Displacement (MD) for Mitsubishi.There is research to develop the system by changing the actual engine displacement by increasing or decreasing the stroke length. Bore/stroke ratio:In reciprocating engines, it is known as either the diameter/stroke ratio (B/S) or the stroke/diameter ratio (S/B), and it is the formula that describes the ratio between diameter and stroke in relation to a cylinder. Square, under-square, over-square, under-square and over-square enginesThe engine is described as a square engine when the engine has a diameter equal to the stroke, that is, the diameter to stroke ratio is exactly 1:1.An engine is described as an oversquare or short-stroke engine if the engine cylinder has a diameter greater than the stroke length and has a diameter-to-stroke ratio greater than 1:1. This design reduces torque but allows the engine to operate at high speeds and generate high peak power. This is the most common design for automobile engines.An engine is described as an undersquare or long-stroke if it has a diameter smaller than the stroke length so that the diameter to stroke ratio is less than 1:1. This design increases piston travel and engine torque, but may reduce the maximum safe speed value. This design is most common in large industrial engines and tractor engines.Rod/stroke ratio:The connecting rod-to-stroke ratio is determined by dividing the connecting rod length, which is the distance from the center of the major end to the center of the minor end along the stroke. This ratio is in the range of 1:1.5 to 1:1.8 for cars. This ratio affects engine dynamics, such as piston speed and acceleration, piston idle time at upper and lower dead points, lateral load on piston, load on cylinder and bearings. Some of these elements affect charge entry, combustion and corrosion.In general, a low ratio means a large connecting rod angle, and this leads to a source of rapid wear of the cylinder walls, piston and piston rings. In the case of a significantly lower ratio, the piston may come out of the cylinder walls due to the large angle of the boom.The high ratio, leads to the lack of air filling the intake manifold at the same speed, and this may lead to weak air flow at slow speeds and weak torque.Compression ratio (CR):The compression ratio of an internal combustion engine is a value that represents the ratio between the volume of the combustion chamber at maximum capacity to minimum capacity. In reciprocating piston engines, it is the ratio of the volume of the combustion chamber when the piston is at the bottom of the stroke (N mH) to the volume of the combustion chamber when the piston is at its highest stroke point (N m). The ratio between the volume before and after compression is called the compression ratio: where:r = compression ratioVs = Swept volume (cylinder volume), Swept volumeVc = clearance volume During this process the pressure and temperature of the gas increase, the compression ratio and the total pressure have a reciprocal relationship as follows:Compression ratio 1:2 1:3 1:5 1:10 1:15 1:20 1:25 1:35Compression ratio 1:2.64 1:4.66 1:9.52 1:25.12 1:44.31 1:66.29 1:90.60 1:145.11 The ratio of compression is defined as the pressure at the upper dead point to the pressure at the lower dead pointpressure ratio = pTDC /pBDC .
Actual values of compression ratios: Spark Ignition Engines, Gasoline Engines: The compression ratio in gasoline engines is often in the range of 1:11. The maximum compression ratio is due to combustion problems, slapping. To overcome this problem in engines with a high compression ratio, gasoline with a high octane number is used. Engines with a ‘ping’ or ‘knock’ sensor and electronic control unit can raise their compression ratio to 13:1.Force-charged engines have a compression ratio of 9.32:1 or less. Engines that run on methanol and ethanol fuels can have a higher compression ratio than gasoline engines. Racing engines that use methanol and ethanol have a compression ratio of over 1:15.Engines that run only on LPG or CNG, the compression ratio may be higher, due to the higher octane number of this type of fuel.Compression ignition engines, diesel engines:In automobile diesel engines the usual compression ratio is 22:1. The appropriate compression ratio depends on the design of the combustion chamber. The ratio is often between 14:1 and 16:1 for direct injection engines and between 18:1 and 23:1 for indirect injection engines. Generally, a higher compression ratio leads to increased power and improved fuel economy, but at the same time, it increases the level of harmful nitrogen oxides (NOx).Variable compression ratio (VCR) engines:Variable compression ratio engines can operate at different compression ratios, according to the needs of the required operating conditions. It can be adjusted to suit different operating conditions such as acceleration, speed, and load. At lower power levels, these engines operate at a high compression ratio, taking advantage of high fuel efficiency without combustion troubles. At higher power levels, these engines are operated at a lower compression ratio to prevent slamming, i.e. the compression ratio is increased at partial loads and decreased at higher loads. The compression ratio in these engines can be changed by several different means, including changing the combustion chamber space, adjusting the height of the piston head, or adjusting the stroke length. fuel air mixture preparation:The mixture needs to be prepared before combustion, this preparation requires mixing the correct proportion of air and fuel, fuel atomization, making the fuel in the form of small drops to ensure a good mixture of air and fuel. This is done for gasoline engines through the feeder or through the injection system. Air-fuel ratio (AF ratio):The correct air-to-fuel ratio is called a stoichiometric mixture. This is the ideal ratio and is 14.7:1 (14.7 parts air to 1 part fuel by weight). In the normal case of an engine, this ratio when all the fuel is mixed with air ensures complete combustion of the mixture. Gasoline engines have an air/fuel ratio between 18:1 at empty load to 12:1 at full load.Lean fuel mixture: It contains more air compared to the fuel, which gives better fuel economy and lower exhaust emissions (17:1).rich fuel mixture: This mixture has a higher proportion of fuel to improve engine capability and cold start (8:1). But this ratio increases emissions and fuel consumption.* Since the density of gasoline = 737.22 kg/m3, the density of air (at 20o Celsius) = 1.2 kg/m3The ratio 14.7: 1 by weight equals 14.7/1.2 : 1/737.22 = 12.25 : 0.0013564Therefore, the ratio is 9030: 1 by volume (one liter of gasoline needs 9.03 m3 of air for complete combustion).
(diesel engines)The air-to-fuel ratio for diesel engines is in the range of 100:1 (100 parts air and 1 part fuel by weight) at empty load speed, 20:1 at full load.Volumetric efficiency VE (hv):It is used for four-stroke engines, which have a clear and distinct intake stroke. Volumetric efficiency = volume of air entering the cylinder / maximum possible volume of the cylinder Volumetric efficiency depends on throttle opening and engine speed as well as the shape of the intake and exhaust system, inlet and outlet openings, valve timing and opening time. The volumetric efficiency of uncharged motors for cars is in the range of 85-90% at the specified speeds. The volumetric efficiency of the charged motors is more than 100%.
Factors Affecting Volumetric Efficiency: The volumetric efficiency is affected by the type of fuel, the air-to-fuel ratio, the mixture temperature, the compression ratio, engine speed, the design of the intake and exhaust system, the ratio of exhaust pressure and intake pressure. The different ways to increase the volumetric efficiency: Methods to increase the volumetric efficiency (VE)* Use larger valves or increase the number of valves.* Make the intake and exhaust inlets more streamlined.* Timing the intake valves and making use of the natural frequency in the exhaust system to help push air in and out of the cylinders. * Using Variable Valve Timing (VVT, VVT-i, VVT-iE), at high speeds the engine needs to open the valves more than the cycle time to allow charge to enter and exit the engine.* The use of Variable Valve Timing and Aperture Amount (VVTL, VVTL-i), is a system that changes the amount and duration of opening in addition to changing the timing. * The use of a dual timing system for both intake and exhaust valves (Dual VVT).* Using the supercharger or turbocharger engine. AnchorValve Timing:Valve timing is the timing of valve opening and closing. Valve timing is measured in degrees relative to the crankshaft. The camshaft, which takes its motion from the crankshaft, controls the opening and closing of the valves. The cam opens the valve by a specified amount (the lift distance) for a period of time. The design of the cam shape and its placement on the camshaft affects the timing, amount and duration of valve opening. Valve timing is affected by camshaft adjustment and valve clearance.Valve timing varies from engine to engine depending on the engine design. The figure shows the timing of the valve opening and closing relative to the crankshaft angles of a four-stroke engine.The intake valve opens at the end of the exhaust stroke before the piston reaches the upper dead point (12o), and remains open until the beginning of the compression stroke after the piston reaches the lower dead point (56o), although the piston is in an upward motion but the charge flow is continuous inertia, which increases the Free cylinder. The opening time for the intake valve is (12 + 180 + 56 = 248 degrees for the crankshaft).The exhaust valve opens at the end of the power stroke before the piston reaches the lower dead point (47o), and then the gases pressure is low and cannot be used to give time for the exhaust gases to escape. It remains open until the beginning of the intake stroke after the piston reaches the upper dead point (21o). The opening time for the exhaust valve is (47 + 180 + 21 = 248 degrees for the crankshaft).The intake and exhaust valves are open together at the end of the exhaust stroke and the beginning of the intake stroke and it is called overlap (33o). Which helps the scavenging quality to get rid of exhaust gases.
AnchorEngine indicator diagrams:The pressure inside the engine with volume can be represented by the so-called pressure-volume pV diagram, and the area inside the curve is represented by the amount of work for the cycle. The pressure curve and pCR crankshaft angles represent the pressure curve within the cylinder at different crankshaft angles. As the figure shows.
Indicated mean effective pressure (imep) or (IMEP):The mean effective pressure graphic is related to the work of the internal combustion engine, and it is an important measure of the engine’s ability to perform work and its value is not affected by the engine capacity. It is the average pressure during one cycle.* The maximum value of the graphic mean pressure for uncharged petrol engines is between 896 and 1103.6 kN/m².
Indicated power (Pi):This power is destined to reach the crankshaft if the mechanical efficiency is 100%. The term “graphing” means that this ability is computed from the graphical curve. Average force (F) acting on the piston per revolution = pressure (p) x area (A) 7.F = p . A (N or kN) Work (W) per turn = force (F) x stroke length (L) W = F. L (N m or J, kN m, kJ) Power (P), work per second = work (W) ÷ time (t) P = W/t (J/sec, or W) Where:imep = average or indicated mean effective pressure (N/m2) or kN/m2 Effective graphic mean pressure =A = area of the piston crown (m2) = area of the piston n = number of engine cylinders = number of cylindersL = piston or engine stroke (m) = stroke lengthN= number of engine revolution per minute per cylinder = speed of engine revolutionLA n = total swept volume of engine, or engine capacity (m3) = engine capacityPi = indicated power (N m/s or W)Ve = engine capacity (m3) = engine capacityk = number of revolution per cycle = number of revolutions per cycle (for a 4-stroke engine k=2, for a 2-stroke engine k=1) = 2 for 4-wheel drive = 1 for dual-motor Engine brake power (Pb):Braking power is the engine’s power measured at the output of the crankshaft at specified crankshaft rotational speeds. The value of the brake power is obtained by using an engine dynamometer at the full throttle opening of the engine. The expression for brake power stems from the fact that the method of measuring engine power in the early days of engine design was using a brake dynamometer. The value of the braking power indicates that the measured braking power is net power or gross power.The values of net power differ from the gross power due to the method of measurement.When testing the engine, the engine power is usually measured without the accessories connected to it, such as the cooling fan, coolant pump, radiator, alternator, and clutch unit, and the engine is connected to a quick exhaust system. Therefore, the amount of power is higher by 10-15%, which is called the gross power compared to the values obtained when measuring the actual engine power with all attachments attached to it, which represents the power produced by the engine of the car and is called the net power.* In Europe, the DIN rating is used, which is to measure the performance of the engine and all accessories are installed on it, so that this gives the net power.* In America the SAE rating is used, which measures total capacity.Gross power is greater than net power by the amount of power needed to operate the engine accessories. The following figure shows the measured torque and power of the engine with and without accessories, to give both the torque and net power values and the torque and total power values in order.
* By comparing the capacity of diesel engines to gasoline engines of equal capacity, we find that the capacity of the diesel engine is less powerful than that of the gasoline engine, because the operating speed of diesel engines is much lower than that of gasoline engines due to the increase in the dimensions and mass of the diesel engine parts to withstand high pressures. * By comparing the capacity of gasoline engines with the electric motor, when you need to install either a gasoline engine or an electric motor in a particular car, we find that the capacity of gasoline engines must be higher than the capacity of the electric motor, as gasoline engines operate at low efficiency, and cars with a gasoline engine need to use Higher power during low-end acceleration at speeds from 0 to 60 km/h. This acceleration can be obtained very efficiently by using an electric motor. Engine torque:Torque (T), equal to the force multiplied by the rotating arm, and accordingly the torque depends on the following factors: the pressure generated within the cylinders, the surface area of the piston affected by the average braking pressure, (so that the force is the product of the pressure times the area), and the effective radius for the crankshaft arm. Engine torque is measured in Newton meters, N m. The torque can be calculated from the general equation for mechanical work as follows:T . θ = F . s (J)whereasF = force (N) forceT = torque (N m)s = distance (m) force effect distance θ = angle (rad)As in the following proof for torque and torque angle:
Or as the figure shows when a tangential force F (N) is applied through an angle θ, when a torque is made through an angle, the distance traveled by the force xy will be equal to r θ where θ is the angle that the crankshaft will travel in radians. torque = force . radius = F. r force x radius =work done = F . distance xy = F . r θ = T . θ work = torque x angle = By applying the equation to the mechanical work of the engine, the work done during one stroke is the amount of torque multiplied by the angle of the crankshaft for the stroke 180o (π). Thus, the equation for work during the power stroke becomes as follows: Mechanical work during power strokeT . π = F . L where L is the stroke length, so the torque produced by one cylinder is Ts = (F×L) / π ……………………………………………….(1) = (bmep. A) x L) / π = bmep. (A × L) / π = bmep. (Vs) / π The torque produced by the engine Te is equal to the sum of the torques produced by all the engine cylinders: Te = n Ts = n (bmep. (Vs) / π) = (bmep. (n . Vs) / π) Te = bmep. (Ve) / π ………………………………………..(2) From equation (2) we find that the value of the generated torque is affected by both the engine capacity and the average effective braking pressure. Doubling the engine capacity will roughly double the engine torque. From equation (1) we find Ts = F× (L / π) = F× (2r / π) = F× (2r / π) = F× R = (bmep). A(×R……..3)where:r = L/2 = crankshaft journal offset (crank radius (throw)) crank radius R = 2r / π = effective (average) arm of torque Relation between engine torque and power:Capacity is the rate at which work is donePower (Pb) = W/t = (T θ)/t = T θ/t = T ω = torque x angular velocity = T (2π N/ 60)Where:Pb = engine brake power (W) = (Watt)T = engine torque (N m) = torque (Nm)N = engine speed (rpm) = engine rotational speed (rpm) Brake mean effective pressure (BMEP):It is an effective measure for comparing the performance of engines with each other. The brake effective average pressure is a theoretical measure and is not related in any way to the actual pressure inside the cylinder. It is simply a powerful tool for comparing engine performance and for differing design and capacity. The braking effective mean pressure is proportional to the graphically effective mean pressure. The average effective brake pressure is calculated from the braking power, which is less than the graphed mean effective pressure by the amount of pressure required to overcome engine friction and loss in flow.The average effective braking pressure is defined as the pressure that, if it affects the pistons equally from the upper dead point to the lower dead point during a power stroke, will result in the measured brake power output. From the power equation we find that Pb = bmep x A x L xnx N/(60 xk) = bmep x Ve x N/(60 xk) From the relationship between power and torque, it is possible to find the relationship between the average brake effective pressure and torquewherePb = Tω = T . 2pN/60ifT = Pb . 60/(2p N) = bmep . Ve Ne/(60 xk) . 60/(2p Ne) T= (bmep) Ve / (2p . k) Where:k = number of revolution per cycle = number of revolutions per cycle (for a 4-stroke engine k=2, for a 2-stroke engine k=1) = 2 for 4-wheel drive = 1 for dual-motor Therefore, the graphic mean effective pressure can be calculated from the previous equations as follows (bmep) = (60. k) Pb / (Ve x N) (bmep) = (2p. k) T/Ve BMEP (kPa) = 12.56637 T (N m) / V (letter) for four-stroke engines BMEP (kPa) = 6.2832 T (N m) / V (letter) for two-stroke engines Actual values of the effective average braking pressure: Brake mean effective pressure (BMEP or bmep) typical valuesFor uncharged spark ignition car engines: the maximum value is in the range of 8.5 to 10.5 bar (850 to 1050 kPa), at the speed at which the maximum torque is.For motors with spark ignition charged cars: the maximum value is in the range of 12.5 to 17 bar (1.25 to 1.7 MPa).For 4-stroke diesel engines, the maximum value is in the range of 7 to 9 bar (700 to 900 kPa).For 4-stroke and supercharged diesel engines, the maximum value is in the range from 14 to 18 bar (1.4 to 1.8 MPa). AnchorEngine friction:Friction is the force that opposes the relative motion of motion, or the intent of motion between two surfaces. Friction within the engine between the rubbing surfaces leads to a loss of engine power, heat generation, wear and lint between the rubbing surfaces. This leads to increased pollutants and increased fuel consumption, decreased performance, and shortened the operational life of the engine and parts.Anchorpumping losses at partial loads for gasoline engines are added to this friction due to the use of the throttle to control the load and speed.
Friction power (Pf):It is the power lost in overcoming friction and the loss in charge flow of an engine. It is equal to the difference between the combustion power inside the cylinder (thread power) and the power coming out of the crankshaft (brake power). Pf = Pi – Pb AnchorMechanical efficiency ME (hm):Mechanical efficiency is the ratio of work out/work in. It is usually expressed as a percentage. It is less than 100% due to the heat loss due to friction.The mechanical efficiency of internal combustion engines can be represented as the ratio between the braking power divided by the graphic power. The mechanical efficiency of the engine = the work leaving the engine / the work entering the engine from the combustion of gases = braking power / rated power Mechanical efficiency = brake power /indicated power (hm) = (Pb)/ (Pi) = (Pi – Pf) / (Pi) = 1 – (Pf/Pi) Where: Pf = power lost in friction = power lost in friction When we substitute the power equation for each of the graphical and braking power into the mechanical efficiency equation, we arrive at that the mechanical efficiency is equal to the ratio between the graphical mean pressure and the graphic mean pressure. (hm) = bmep/imep The loss in flow and the friction between the piston rings and the cylinder walls account for the greatest frictional work and lost power. The main factors that contribute to the loss of power and the reduction of the output power of the engine:1- The type of metal used in abrasive surfaces and finishing (surface smoothness).2- Loading between abrasive surfaces and the lubrication condition.3- The speed of friction.4- Compression ratio.5- The rate of friction (number of revolutions per minute – engine rotational speed).6- throttle position7- Air resistance, the air resistance increases with the square of the velocity. Flywheel, clutch, alternator, cooling fan.8- Stirring the lubricating oil. The figure shows the value of the graphic power extracted from measuring the pressure inside the engine, the braking power measured from the engine output, the amount of frictional power (the difference between the rated power and the braking power), and the mechanical efficiency (the quotient of the brake power/graphic power) with the engine’s rotational speed. * From the figure it is shown that the rated power (Pi) is higher than the braking power (Pb) over the engine speed range. When measuring the difference between the two capacities at each speed, we find that this difference represents the loss in power due to flow and friction (Pf) at this speed. As the speed increases, the lost power increases, and thus the difference between the two power curves increases.
Engine power-to-weight ratio P-to-w (specific power):An engine’s power-to-mass ratio, specific power, or power-to-mass ratio is a mathematical method usually applied to engines to help compare them. This ratio is a measure of the actual performance of any engine. Power to weight ratio for single cylinder and multi cylinderPower to weight ratio (single-and multi-cylinder engines):Whereas, engine power varies with the square of the diameter (piston area) and mass changes with the cube of the diameter (change in volume). Increasing power by using a larger cylinder leads to a lower power/weight ratio, but increasing the number of cylinders keeps the power/weight ratio the same. This means that if the power of the 4-cylinder engine is equal to that of the 6-cylinder engine, the power/weight ratio of the 6-cylinder engine will be higher (better). The power/weight ratio is calculated by dividing the engine’s power (maximum value) by the engine’s weight (or engine mass) P-to-w = P/w It is measured in kilowatts/kg or any of the following units: kW/kg, PS/kg, hp/kg * For four-stroke gasoline engines, the ratio is between 0.25-0.35 kilowatts/kg, and for Wankel engines, the ratio is 1.5 kilowatts/kg. Engine power per unit capacity ratioAnchorSpecific engine output (Engine power/unit displacement):It is measured in kilowatts/liter or any of the units kW/l, PS/l, hp/l, and is calculated by dividing the engine’s power by its capacity. This ratio is useful when comparing different engines, including finding the limits of stress affecting the engine. In the case of high values, this indicates that the engine is subjected to high stresses, and this indicates a shortened engine life. Gasoline engines have higher values than diesel and rotary engines have a higher percentage of gasoline, and the value increases by 1.25-2 for charged engines. Fuel consumption (FC):The fuel an engine consumes can be measured by volume or mass. By volume, the unit is cubic centimeters or liters per second, minute or hour (1000 cm3 = 1 liter). Measured by mass, the unit is kilograms per second, minute, or hour (1 liter of water equals 1 kilogram at 4°C)The relationship between consumption by volume and consumption by mass is Fuel Consumption (kg/min) = Fuel Consumption (l/min) x Fuel Specific Density (kg/l) *Fuel Density:The unit kg/m3 is usually used to indicate the density of a fuel at 25°C:Ethanol 789.0, Methanol 791.5, Gasoline 702.5, Propane 510.0, Hydrogen 70.8, Diesel 900. Back to the list Specific fuel consumption (SFC):Specific fuel consumption is the mass or volume of fuel that an engine consumes per hour to produce a kilowatt of power. The unit used to denote the specific consumption is kg/(kilowatt hour). SFC = FC/engine power (kg/h)/kW, (kg/kW h) There are two types of specific consumption, the specific consumption of the brake, in which the fuel consumption is attributed to the braking power of the engine, and the specific consumption, in which the fuel consumption is attributed to the power rating of the engine.It is considered an indicator of engine thermal efficiency, and is one of the most important properties of an engine. A comparison can be made between engines of different power and characteristics, as long as a single measurement method is available under the same operating conditions. The specific fuel consumption curve with respect to the engine speed represents the reflection through a mirror of the thermal efficiency curve, and the lowest point in the specific fuel consumption curve is the highest point in the thermal efficiency curve. The minimum specific fuel consumption for gasoline engines is in the range of 300 g/kWh and 83 g/MJ, regardless of any particular design. In general, the specific fuel consumption will decrease with the increase in the compression ratio. Diesel engines are in the range of 240 g/kWh. This means that diesel engines have better specific fuel consumption than gasoline (low value indicates better fuel consumption) as they have a higher compression ratio. Car fuel consumption rating:For cars, average fuel consumption is measured by the volumetric fuel unit traveled: mile per gallon (mpg), kilometer per liter (km/L), or liter per 100 km. (L/100 km). The reason for the increased fuel economy for diesel cars is that diesel engines use a super lean air fuel ratio, which is an extremely high compression ratio, and diesel fuel has a high heat value of fuel. Thermal efficiency (hth):The thermal efficiency of the engine is defined as the engine’s efficiency in converting the thermal energy contained in the fuel into mechanical energy. Thermal equilibrium tests have clearly shown that internal combustion engines are not efficient in this conversion process. The thermal efficiency of diesel engines may reach 41%, but it is usually in the range of 30%, and gasoline engines may reach 37.3%, but it is usually in the range of 20%.The thermal efficiency can be obtained from the equation whereCV is the calorific or heat value of 1 kg of the fuel (J/kg, kJ/kg or MJ/kg) whereρ is the relative density (kg/L) of the fuel. Fuel Density (kg/L)BSFC is the brake specific fuel consumption (kg/Pb h) Also, the ISFC graphic specific fuel consumption isIndicated thermal efficiency = hth = * The thermal efficiency of the engines does not reach 100% due to the thermal loss of energy extracted from the fuel, which is represented in the energy lost in cooling water, and energy lost in exhaust gases (hot), as shown in the form of the thermal equilibrium of the engine.
Calorific value of fuel (CV)It is the amount of heat produced by the combustion of fuel under constant pressure and under normal operating conditions. The calorific value is expressed in units of kilojoules/kg (kJ/kg) or kilojoules/m3 (kJ/m3).There are two calorific values for fuel, the maximum or total calorific value and the minimum or net calorific value.Higher Calorific Value (or Gross Calorific Value- GCV), considers that the water vapor from the combustion has fully condensed and the heat in the steam has been recovered.Lower Calorific Value (or Net Calorific Value- NCV), considers that the heat in the water vapor from combustion is not recovered.Normally the calorific value of solid and liquid fuels is the highest calorific value under constant volume. As for the calorific values of gaseous fuels, they are the highest calorific value under constant pressure.The table shows the approximate values of the calorific values of the fuel:Solid and liquid fuels Gaseous, liquid and solid fuels Gross calorific value/ MJ kg−1The highest calorific value is megajoules/kgAlcohol Ethanol Ethanol30Methanol Hydrogen hydrogen 23140 Petroleum and petroleum products Diesel fuel 46Kerosine 47Petrol Gasoline 44 Engine performance curve:
Factors affecting the engine torque and power:Ignition problems: pre-ignition, slap detonationTuning problems: weak fuel mixture, ignition timing-retarded ignition, camshaft advanced or crankshaft retardation, camshaft advanced or crankshaft retarded, tappet clearances, fuel injection pump timingOperating conditions: engine load,Motor design: variation of compression ratio, motor supercharging, piston speed
Supercharged petrol engine (high charge) Supercharged petrol engine (low pressure control)Supercharged petrol engine High degree of boost
Supercharged petrol engineWith low pressure control boost
Engine types and classifications :There are many ways to classify engines even though the basic parts of all engines are the same (engine block, pistons, crankshaft, camshaft…..). But designs differ, which affects how they perform and maintain. Modern engines for cars can be classified as follows: Arrangement of cylinders In-line engine V-shaped V-type engine Slant engine – Opposed engine* Number of cylinders: Four cylinders Six cylinders Eight cylinders – and as few as 3, 5, 12 or 16 discs* Cylinder numbers The cylinders for the engines are numbered in a straight line 1 2 3 4 V-shaped engines can recognize cylinder number 1, which is slightly ahead of the opposite cylinder on the other side. In most cases, the odd numbers (1 3 5) are on one side and the even numbers (2 4 6) on the other side. In some engines, the cylinders are numbered in order on one side (1 2 3) and the other side (4 5 6). You must refer to the catalog to verify this information.*Firing order: 4-cylinder engine (1-3-4-2) or (1-2-4-3) – Engine more than 4 cylinders, refer to the catalog for arrangement.* Cooling system: Liquid cooling system (water plus coolant) called water cooling system. Liquid cooling Air cooling system. Air cooling* Fuel system: Gasoline engines – Feeder Carburetor Gasoline injection Diesel engines Anchor Alternative fuel engine* Ignition system: Spark ignition (SI) system Compression ignition (CI) system* Combustion chamber shape: Pancake (bath tub) combustion chamber Wedge combustion chamber Hemispherical combustion chamber (hemi) Semi-hemi combustion chamber Swirl combustion chamber Crossflow combustion chamber Non cross flow (backflow) combustion chamber Two-valve combustion chamber Four-valve combustion chamber Mixture jet combustion chamber Air jet combustion chamber Stratified charge combustion chamber Precombustion chamber* Camshaft drive method: Cogged rubber belt Gear Chain . chain Valve location: In the engine body (cylinder block) In the cylinder head (OHV)Camshaft position: Cam-in-block Overhead cam* Number of camshafts: Single overhead cam Dual overhead cam* Method of air (mixture) delivery Normal aspiration Super charging (mechanically driven blower) Turbo charging (exhaust driven blower)* Alternate engines: Two-stroke engine Wankel (rotary) engine Gas turbine engine Stirling engine Main parts of Engine construction and components :cylinder head Engine upper end(Valve covers, valves, camshaft, cylinder heads, valve guides, valve closing springs, valve lifters, …) Engine front end(Camshaft drive assembly, damping and balancing system, intake manifold, exhaust manifold, timing system..) Engine lower end (cylinder block)(cylinder block, crankshaft box, crankshaft, pistons, connecting rods, bearing, flywheel, oil pan) Engine operating systems :Charging system Fuel system Ignition system Exhaust system Cooling system Lubricating system Engine management and control system Emission control system Charging system Starting system Engine position in the car Front engine Rear engine Central (mid) engine
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