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Spark-Ignition Engine Combustion
Published in Kenneth M. Bryden, Kenneth W. Ragland, Song-Charng Kong, Combustion Engineering, 2022
Kenneth M. Bryden, Kenneth W. Ragland, Song-Charng Kong
From a combustion perspective, an internal combustion engine consists of multiple piston-cylinders, each with separate intake and exhaust valves and a spark plug. After the spark plug fires, a turbulent flame front propagates outward from the spark plug. The combustion then releases energy from the fuel and creates elevated pressure against the piston and connecting rod, thus producing torque on the drive shaft. The piston travels in a repetitive cycle between being fully inserted at top dead center (TDC) and being fully withdrawn at bottom dead center (BDC). The four-stroke engine sequence for a cylinder (Figure 7.1) is as follows: (1) With the intake valve(s) open and exhaust valve(s) closed, a mixture of air and fuel is drawn into the cylinder as the piston moves downward toward BDC; (2) with all valves closed, the fuel–air charge is compressed as the piston moves upward toward TDC; (3) the spark discharges when the fuel–air mixture is nearly fully compressed, and the power stroke occurs as the charge combusts rapidly, forcing the piston downward toward BDC due to the high pressure in the cylinder; and (4) as the piston nears BDC, the exhaust valve opens and the piston then moves upward toward TDC while expelling the combustion products. The cycle is repeated continuously with the power stroke occurring during every other revolution of the drive shaft.
Introduction to Internal Combustion Engines
Published in K.A. Subramanian, Biofueled Reciprocating Internal Combustion Engines, 2017
A four-stroke engine is an IC engine in which the piston completes four separate strokes while turning a full rotation of the crankshaft. A stroke refers to movement of piston either traveling from TDC to BDC or vice versa. Four-stroke completions correspond to a 720-degree crank angle and completion of two revolutions of a flywheel. One stroke almost completely executes each process, such as suction, compression, expansion, and exhaust, and each stroke corresponding to each process is called a suction stroke, compression stroke, expansion stroke, and exhaust stroke. One cycle has four strokes and theoretically each stroke has a corresponding 180-degree crank angle rotation of a flywheel. A four-stroke engine has many advantages over a two-stroke engine in terms of higher thermal efficiency and less emissions, because sufficient time is relatively available for each process in a four-stroke engine compared to a two-stroke engine. The valve timing diagram of a four-stroke cycle engine is given in Figure 4.5.
UAS Propulsion System Design
Published in R. Kurt Barnhart, Douglas M. Marshall, Eric J. Shappee, Introduction to Unmanned Aircraft Systems, 2021
Michael T. Most, Graham Feasey
Four-stroke engines afford certain design benefits: less vibration (in comparison to a two-stroke engine), quieter operation, relatively high torque, and a broader power band. When range and endurance are important factors in the anticipated mission of the UAS, four-stroke engines offer the major advantage of providing the higher fuel efficiency than two-stroke internal combustion engines. On the other hand, they are also generally heavier, more complex, and expensive than two-cycle engines. Four-stroke aviation engines have relatively high compression ratios that require higher octane fuel to prevent preignition of the fuel. Aviation engines use aviation gasoline (AVGas) that uses tetraethyl lead (TEL) to boost octane number.
Numerical analysis of modified crossbreed engine cycle under BS VI norms
Published in International Journal of Ambient Energy, 2022
P. V. Elumalai, M. Parathasarathy, S. Sathishkumar, M. Murugan, A. Saravanan, M. Sreenivasa Reddy, Keerty Venkata Sri Ramachandra Murthy
In the conventional IC engine, chemical energy is converted into useful mechanical energy by way of combustion of fuel, which produces a larger amount of energy, and only up to 35%–40% power is successfully transmitted to the engine output shaft due to its additional operating and moving parts. The major disadvantage of a four-stroke engine is the power loss during the valve train operation and the overall weight of the engine (Abdullah et al. 2013). Moreover, a four-stroke engine has only one power stroke per cycle, thus it produces only half the power compared to a two-stroke engine.