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Internal Combustion Engines
Published in Iqbal Husain, Electric and Hybrid Vehicles, 2021
The sketch of a representative reciprocating IC engine including the terms standard for such engines is given in Figure 13.1. The engine consists of piston that undergoes a reciprocating motion within the engine cylinder. The position of the piston at the bottom of the cylinder when the volume inside is maximum is known as the bottom dead center (BDC). The position of the piston at the top of the cylinder when the volume inside is minimum is called the top dead center (TDC). This cylinder minimum volume when the piston is at the TDC is known as the clearance volume. A crank mechanism converts the linear motion of the piston into rotary motion and delivers the power to the crankshaft. The volume swept by the piston as it moved from the TDC to the BDC is known as the displacement volume, which is a parameter commonly used to specify the size of an engine. The compression ratio is defined as the ratio of the volume at BDC to the volume at TDC.
Shaft Engines
Published in Ahmed F. El-Sayed, Aircraft Propulsion and Gas Turbine Engines, 2017
Figure 6.9 is a sketch of a reciprocating internal combustion engine consisting of a piston that moves within a cylinder fitted with two valves. The sketch is labeled with some special terms. The bore of the cylinder is its diameter. The stroke is the distance the piston moves in one direction. The piston is said to be at top dead center (TDC) when it has moved to a position where the cylinder volume is at the minimum [3]. This minimum volume is known as the clearance volume. When the piston has moved to the position of maximum cylinder volume, the piston is at bottom dead center (BDC). The distance between the TDC and the BDC is the largest distance that the piston can travel in one direction, and it is called the stroke of the engine. The volume swept out by the piston as it moves from the top dead center to the bottom dead center position is called the displacement volume. The reciprocating motion of the piston is converted to rotary motion by a crank mechanism.
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
Two-cycle engines complete the same five events (i.e., intake, compression, ignition, power, and exhaust) required of any practical heat engine, but in just two piston strokes and 360° of crankshaft rotation. Although slightly more complex two-cycle designs exist (e.g., those using rotary and reed valves), the simplest construction requires no valves and very few parts. As the piston begins upward on the compression stroke, a low pressure area is created below the piston. Occupied by the piston connecting rod and the crankshaft, this area is enclosed and termed the crankcase. Air, mixed with fuel in the proper mixture ratio and a small amount of oil for lubrication, is drawn into the crankcase and stored. At the same time, above the piston is a charge of air and fuel, previously stored in the crankcase during the preceding compression stroke, which is being compressed by the upward motion of the piston. The ignition event is timed at the proper point around the maximum upward travel of the piston (TDC) to provide maximum expansion of the gases and the greatest downward force on the piston through the connecting rod to the crankshaft. This is the power stroke. With the downward travel of the piston, an exhaust port is uncovered to begin the scavenging of the cylinder. As the piston continues downward, an intake port is uncovered and the decreasing crankcase volume forces the fuel/air mixture stored there through the intake port and into the cylinder. The fresh charge pushes the remaining spent gases out of the cylinder through the exhaust port. The intake port and then the exhaust port are covered by the piston as the fresh charge is compressed and the process is repeated so long as the engine continues to operate. Thus, the two-stroke engine is capable of completing all five events in one complete crankshaft rotation.
Effects of Dilution and Flammability Changes on Mixture Reactivity in a Natural Gas Internal Combustion Engine
Published in Combustion Science and Technology, 2023
A. U. Bajwa, T. Linker, M. A. Patterson, G. Beshouri, T. J. Jacobs
To explain the combustion phasing results shown in Figure 5, various combustion event durations are shown as a function of LFS at TDC in Figure 10. TDC is selected as a reference because it precedes most combustion milestones and can be considered a time datum within the flame initiation period. The slope and correlation coefficients of the combustion event duration and LFS results are also shown. These are used to highlight the average magnitude of combustion event duration shortening as LFS increases and the strength of LFS in driving these changes, respectively. Going from Figure 10(a) to Figure 10(c), the slope, which is the CAD-reduction in combustion event duration for every m/s increase in LFS, increases in magnitude by around 100%. This confirms that the effects of combustion variations on the overall combustion rate become more pronounced as combustion progresses. Moreover, the strong negative correlation between LFS and combustion event durations indicates that variations in the flame initiation (Figure 10(a)) and propagation (Figure 10(b, c)) periods are caused by LFS changes. Figure 10(d) and 10(e) show the isolated effects of LFS at TDC on CA10-50 and CA50-70. The small combustion event shortening rate values (slopes) indicate that the effect of LFS increase on combustion rate increase becomes less pronounced during the latter stages of combustion.
W-Ti-N thin film tribological behaviour for piston skirt properties improvement
Published in Surface Engineering, 2021
Khaled Chemaa, Salim Hassani, Mohammed Gaceb, Noureddine Madaoui, Abdelhamide Guebli
The internal combustion engines industry today requires engines with better characteristics such as improved tribological properties i.e. reduced friction and wear. Richardson [1] reported that energy losses by friction represent about 4–15% of the total energy used in a diesel engine. Piston assembly contributes to about 40–50% of that energy loss. Within that amount, piston skirt contribution is about 25–47%. Furthermore, an estimation done by the US department of energy suggests that in heavy duty vehicles, the total energy losses because of friction consume about 160 million barrels of diesel fuel per year [2]. Concerning wear, it occurs generally on piston skirt surface when the contact between piston skirt and liner becomes dry or boundary. This occurs when the piston reaches the Top Dead Centre (TDC).
Relationship between acoustic emission signal and loads on pneumatic cylinders
Published in Nondestructive Testing and Evaluation, 2020
Houssam Mahmoud, Pavel Mazal, Frantisek Vlasic
The valve is opened by a digital input, and the air starts entering through port B in the rear cap to the damping area, the air passes around the cushion throttle and then through the throttle nozzle to the space between the cushion seal lip and the damping rear piston. When the minimum required pressure is reached the piston starts moving from the BDC (bottom dead centre), and the piston extends to reach the TDC (top dead centre). The cushion head piston pushes out the air to expel it through port A in the head cap. The damping phase starts when the head damping piston touches the head seal cushion at a distance of 21.7mm. In the damping phase the air is pushed through the throttle nozzle only, until the piston reaches the TDC. The end of the progress stroke is when the head cushion piston impacts the head cushion cap. The air is supplied from Port B during this stroke and the air of chamber A is vented to the atmosphere as shown in Figure 3.