Four-Stroke Cycle Engine

With the intake valve open, the piston movement to the right creates a low pressure region in the cylinder, which causes air and fuel to flow through the intake valve to fill the cylinder. 

The intake valve is now closed as the piston moves from the bottom dead center (BDC) to top dead center (TDC), compressing the fuel/air mixture. At Point 3, just prior to TDC, a spark ignites the fuel/air mixture and the resulting combustion causes the pressure and temperature to begin a very rapid rise within the cylinder. 

Burning continues as the piston reverses at TDC and pressure rises through the first portion of the power or expansion stroke. It is the increase in pressure due to burning the fuel that forces the piston to the right to produce useful mechanical power. The piston moves to the right until BDC is reached. 

With the exhaust valve open, the upward stroke from BDC to TDC creates a positive pressure within the cylinder, which forces combustion products from the cylinder on the exhaust stroke. 

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Both two- and four-stroke cycle engines are used in commercial applications. For the purpose of this discussion, however, comments will be limited to applications normally encountered in the oil and gas industry. Some of the advantages and disadvantages associated with each engine type are as follows ... 

Four-stroke cycle engine An engine completing one cycle in four strokes of the piston or two shaft revolutions. The cyclic events are designated by the following strokes (1) induction or suction stroke, (2) compression stroke, (3) power or expansion stroke, (4) exhaust stroke. ... 

Engine types fall into two categories two-stroke cycle and four-stroke cycle. Typical two-stroke-cycle engine arrangements are shown in Figs. 6.87 and 6.88. A typical four-stroke-cycle engine arrangement is shown in Fig. 6.89. 

Both gasoline and diesel engines are available in either a two-stroke- or a four-stroke-cycle design. The fundamental difference between the Otto engine cycle (named after Nikolaus Otto, who developed it in 1876) and the diesel engine cycle involves the conditions of the combustion. In the Otto cycle. 

Figure 15.1 Four-stroke cycle for an internal combustion engine...

Jones, B., etal., A Comparative Analysis of Ethanol Versus Gasoline as a Fuel in Production Four-Stroke Cycle Automotive Engines, SAE Paper No. 952749, Society of Automotive Engineers, Warrendale, Pa., 1995. 

Service category CG-4 designated to meet 1995 exhaust emission standards for use in high speed four-stroke-cycle diesel engines New classification for the generation of heavy-duty engine oils. The process of adsorption characterized by a chemical reaction between the adsorbate and adsorbent, where exchange of orbital electrons occurs. 

By their design, two-stroke engines have different lubrication requirements from four-stroke automobile engines. Two-strokes rely on lost oil lubrication where a continuous feed of lubricant into the engine is burned or lost and replenished every cycle. This lubricant may be either pre-mixed with the fuel or injected via a small metering delivery pump into the engine as a function of throttle position. Two-stroke lubricants must have a number of important attributes, mainly ... 

The diesel engine works following a four-stroke cycle analogous to that of a petrol engine. There are however, very important differences, which can be explained using... 

Most internal-combustion engines operate on a four-stroke cycle (see Figure 12-13). 

The car engine still in use in the majority of motor transport is based on the four-stroke cycle developed by Nikolaus Otto in the 19th century. This cycle places key requirements on the fuel at the various stages (Figure 10.63). 

Figure 10.63 The stages of the four-stroke cycle of a gasoline engine...

The Otto cycle is essentially the cycle describing the internal-combustion automobile engine. This is a four-stroke cycle, in contrast to the simpler two-stroke Carnot cycle and the various others, such as the Stirling and Brayton cycles, that operate on a single oscillation of the piston. The Otto cycle consists of an intake expansion, a compression, an expansion resulting from ignition... 

The four-stroke cycle spark ignition (SI) internal combustion engine (ICE) was initially proposed by Beau de Rockas in 1862 and first built by N. A. Otto in 1876. This engine has become the major piston engine in use today. The PV cycle of the engine is shown in Fig. 4.3 where the four strokes are indicated. 

Figure 11.6. P-Vq diagram for four-stroke cycle IC engine (Otto cycle).

Reciprocating engines are available in two basic types—two-stroke or tour-stroke cycle. Regardless of the engine type, the following four f unctions must be performed in the power cylinder of a reciprocating engine ... 

Pressure-volume curve illustration for a turbocharged and direct-injected high-speed heavy-duty four-stroke diesel cycle engine. 

Toward the end of the nineteenth centuiy, successful two-stroke engines operating on the Otto cycle were developed by Dugald Clerk, James Robson, Karl Benz, and James Day. In this engine, the intake, combustion, expansion, and exhaust events all occur with but two piston strokes, or one crankshaft revolution. In principle this should double the output of a four-stroke engine of equal piston displacement. However, instead of the intake and exhaust events taking place during sequential strokes of the piston, they occur concurrently while the piston is near BDC. This impairs the ability of the... 

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