LEC 1 - Chapter 1 - Part 1 PDF

Internal Combustion Mechanical Power Engineering Dept. Faculty of Engineering, Mataria, Helwan University 4th Year Lecture 4th Year, 2024-2025 Dr. Mohamed Elmously 10/2/2024 ‫قسم هندسة القوي الميكانيكية – هندسة المطرية‬ 1 Grade Distribution (65 ) Clas...

Internal Combustion Mechanical Power Engineering Dept. Faculty of Engineering, Mataria, Helwan University 4th Year Lecture 4th Year, 2024-2025 Dr. Mohamed Elmously 10/2/2024 ‫قسم هندسة القوي الميكانيكية – هندسة المطرية‬ 1 Grade Distribution (65 ) Class attendance 5 Grade Quizs 5 Grade Mid-term 20 Grads Oral Exame 20 Grads Lab Presentations 15 Grads Final exam 15th week 60 Grads 10/2/2024 ‫قسم هندسة القوي‬ 2  AGENDA Course Content.? 1. Engine Classifications 2. Engine Cycles 3. Engine Performance 4. Combustion in Spark Ignition Engines 5. Engine Emissions 6. Combustion in Spark Ignition Engines 7. Biodiesel Vehicles 10/2/2024 ‫قسم هندسة القوي الميكانيكية – هندسة المطرية‬ 3  ‫‪LECTURE 01‬‬ ‫‪10/2/2024‬‬ ‫قسم هندسة القوي الميكانيكية – هندسة المطرية‬ ‫‪4‬‬ Introduction Heat Engines Heat engines may be conveniently grouped into two principal classes as follows These are generally used for driving locomotives, ships, generation of electric power etc  Heat Engines External Combustion Engines. In this case, combustion of fuel takes place outside the cylinder, as in case of steam engines where the heat of combustion is employed to generate steam which is used to actuate a piston in a cylinder. Other examples of external combustion engines are steam turbine and gas turbine. Internal Combustion Engines. In this case combustion of the fuel with oxygen of the air occurs within the cylinder of the engine. The internal combustion engine group includes: ❑engines employing mixtures of combustible gases and air, known as gas engines. those using lighter liquid fuels, known as petrol engines ❑and those using heavier liquid fuels, known as oil, compression ignition engines or diesel engines. Principles of Internal Combustion Engines  Principles of Internal Combustion Engines It should have high strength to withstand high pressure above 50 bar and temperature above 2000oC The ordinary engine is made of cast iron heavy duty engines are made of steel alloys or aluminum alloys It is in direct contact with the products of combustion so it must be cooled Principles of Internal Combustion Engines Conventional internal combustion engines have one or more cylinders in which combustion of the fuel takes place. A cross-section of an engine cylinder with the principal parts labeled is shown in the Fig. Principles of Internal Combustion Engines 1. Cylinder block 2. Cylinder head 3. Inlet and exhaust valves Inlet valve is meant for admitting air or mixture of fuel and air to the engine cylinder Exhaust valve is meant for discharging the products of combustion at appropriate time 4. Piston 5. CamShaft 6. Connecting rod 7. Crankshaft 8. Flywheel Principles of Internal Combustion Engines Cylinder: It is a cylindrical shaped container within which a piston travels in a reciprocating linear motion. It should have high strength to withstand high pressure above 50 bar and temperature above 2000oC. The ordinary engine is made of cast iron. heavy duty engines are made of steel alloys or aluminum alloys. It is in direct contact with the products of combustion so it must be cooled. For cooling of cylinder a water jacket (for liquid cooling used in most of cars) or fin (for air cooling) are situated at the outer side of cylinder. Principles of Internal Combustion Engines Cylinder block The cylinder is supported in position in the cylinder block, attached to, or an integral part of the crankcase. Cylinder head: Top end of the cylinder is enclosed by the cylinder head. The cylinder head generally bolted to the cylinder block. A copper or asbestos gasket is provided between the engine cylinder and cylinder head to make an airtight joint. Principles of Internal Combustion Engines Inlet and exhaust valves: These valves are incorporated in the cylinder head. The number of valves in an engine depends on the number of cylinders as two valves are used for each cylinder. 1. Inlet valve is meant for admitting air or mixture of fuel and air to the engine cylinder. 2. Exhaust valve is meant for discharging the products of combustion at appropriate time. The valves are normally kept closed by means of cams geared to the engine shaft. The valves are fitted in the port at the cylinder head by use of strong spring. This spring keep them closed. Both valves usually open inwards. Principles of Internal Combustion Engines Piston: Transmit the force exerted by the burning of charge to the connecting rod. It is usually made of aluminum alloy which has good heat conducting property and greater strength at higher temperatures. Ports and manifolds: The passages in the cylinder head leading to the valves are called ports. The system of pipes which connects the inlet ports of the various cylinders to a common, air or air-fuel intake for the engine is called the inlet manifold. Thus, a system connecting exhaust ports to a common exhaust pipe is known as exhaust manifold. Principles of Internal Combustion Engines Connecting rod: Connecting rod connects the piston to crankshaft and transmits the motion and thrust of piston to crankshaft The shape and size of crankshaft depends on the number and arrangement of cylinders It is usually made by steel forging Crankcase: The main body of the engine to which the cylinders are attached, and which contains the crankshaft and crankshaft bearings is called the crankcase This member also holds other parts in alignment and resists the explosion and inertia forces It also protects the parts from dirt etc serves as a part of lubricating system and sometime it is called oil sump Principles of Internal Combustion Engines Flywheel: It is a big wheel mounted on the crankshaft, whose function is to maintain its speed constant. It is done by storing excess energy during the power stroke, which is returned during another stroke. Basic geometry of reciprocating I.C.E Basic geometry of reciprocating I.C.E Cylinder bore (D) : The inside diameter of the cylinder is called bore and is measured in centimeters or millimeters Piston area (A) : The area of circle of diameter equal to the cylinder bore Stroke (L) : As piston reciprocates inside the engine cylinder, it has got limiting upper and lower positions beyond which it cannot move, and reversal of motion takes place at these limiting positions Top dead centre (TDC): The position of the cylinder, when it is closest to the top of the cylinder, is called top dead centre Bottom dead centre (BDC): The position of the piston, when it is farthest from the top of the cylinder, is called bottom dead centre  Basic geometry of reciprocating I.C.E Clearance volume (Vc): The volume confined in the cylinder above the top of the piston, when the piston is at top dead centre, is called the clearance volume and is usually measured in cubic centimeters or liters Displacement volume or Swept volume (Vd): The volume swept through by the piston in moving between top dead centre and bottom dead centre, is called the piston displacement Cylinder volume (Vt): Total volume of the cylinder when piston is at the bottom dead centre Total cylinder volume = Swept Volume + Clearance volume Basic geometry of reciprocating I.C.E Compression ratio (r): The ratio of volume when the piston is at the bottom dead centre (i.e. cylinder volume) to the volume when the piston is at top lead centre (i.e. clearance volume) is called the compression ratio. r = Vt / Vc r = (Vd + Vc) / Vc Basic geometry of reciprocating I.C.E  ‫ أهمية نسبة االنضغاط‪:‬‬ ‫‪.1‬زيادة الكفاءة الحرارية‪ :‬كلما زادت نسبة االنضغاط‪ ،‬زادت كفاءة‬ ‫المحرك من حيث تحويل الطاقة الحرارية إلى طاقة ميكانيكية‪.‬ذلك ألن‬ ‫زيادة نسبة االنضغاط تؤدي إلى زيادة درجة حرارة وضغط خليط الوقود‬ ‫والهواء قبل االحتراق‪ ،‬مما يعزز كفاءة االحتراق‪.‬‬ ‫‪.2‬زيادة القوة‪ :‬نسبة االنضغاط األعلى تعني أن المحرك يمكنه إنتاج طاقة‬ ‫أكبر مع نفس الكمية من الوقود‪ ،‬وهذا يؤدي إلى تحسين األداء وزيادة القوة‬ ‫الناتجة عن المحرك‪.‬‬  ‫تأثير زيادة نسبة االنضغاط‪:‬‬ ‫تحسين الكفاءة‪ :‬عند زيادة نسبة االنضغاط‪ ،‬تزداد الكفاءة الحرارية للمحرك‪ ،‬مما يقلل من‬ ‫استهالك الوقود لكل وحدة طاقة منتجة‪.‬‬ ‫كثيرا‪ ،‬قد يتعرض المحرك‬‫ً‬ ‫احتمالية حدوث الطرق ( ‪Knocking):‬إذا زادت نسبة االنضغاط‬ ‫لظاهرة الطرق‪ ،‬وهي حدوث احتراق غير متحكم فيه لخليط الوقود والهواء قبل الوقت المناسب‪.‬‬ ‫هذه الظاهرة تؤدي إلى أضرار في المحرك إذا لم تتم السيطرة عليها‪.‬‬ ‫تأثير تقليل نسبة االنضغاط‪:‬‬ ‫انخفاض الكفاءة‪ :‬نسبة انضغاط أقل تؤدي إلى تقليل الكفاءة الحرارية‪ ،‬مما يعني أن المحرك‬ ‫سيستهلك المزيد من الوقود إلنتاج نفس الكمية من الطاقة‪.‬‬ ‫تقليل خطر الطرق‪ :‬نسبة االنضغاط األقل تساعد في تقليل احتمالية حدوث الطرق‪ ،‬ولكنها تأتي‬ ‫على حساب الكفاءة واألداء‪.‬‬ Basic geometry of reciprocating I.C.E Square engine: An engine that has equal, or nearly equal, bore and stroke dimensions. Square engines are commonly used in spark-ignition (SI) passenger cars. Under-square engine: An engine with a stroke dimension that is longer than the bore dimension, also known as a long-stroke engine. These engines are used to perform heavy hauling and vocational work, such as diesel or SI engines used in pick-up trucks. Basic geometry of reciprocating I.C.E Over-square engine: An engine with a stroke that is shorter than the bore diameter. Over-square engines are best suited to high-speed operation. Stroke ratios in over-square engines are better adapted to use in high-speed applications where engines need to develop the highest torque at high speed. Over-square engines, also called short-stroke engines, are commonly used by cars with SI systems.  Part 2: Engine Classifications