Four-stroke engines

Whereas automobile companies continue to improve the four-stroke engine, making it more efficient and more powerhil to mn vehicles that are smaller and lighter and have sufficient space, the two-stroke and the lean bum engines are also being studied. 

Reduced weight over similar horsepower four-stroke engines. 

In France in 1862, Beau de Rochas outlined the principles of the four-stroke engine so common today. ITowever, he never transformed those principles into hardware. Among the improvements proposed by de Rochas was compression of the charge prior to combustion. In contrast, the charge in the Lenoir engine was essentially at atmospheric pressure when combustion was initiated. 

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... 

If the crankcase compression illustrated in Figure 5 is used, the reservoir of lubricating oil normally contained in the crankcase of a four-stroke engine (sec Figure 1) must be eliminated. Cylinder lubrication is then usually accomplished by mixing a small quantity of oil into the fuel. This increases oil consumption. An alternative allowing use of the... 

Barlow, K. A. (1994—1995). Nikolaus August Otto and the Four-Stroke Engine. Transactions of the Newcomen Society 66 suppl. no. 1. 

The internal combustion engine can be operated as a two-stroke or a four-stroke engine. 

The four-stroke engine requires four piston strokes (or two crankshaft revolutions) for each cycle. In a downward stroke, the intake valve is opened and the combustible mixture is brought into the cylinder. In an upward stroke the fuel-air mixture is compressed and ignited near the top of the stroke. This forces the piston downward (to provide power). In the next upward stroke the exhaust valve is opened and the spent gases are forced from the cylinder. In the following downward stroke, the cycle is repeated with the opening of the intake valve. 

Crankcase oil or motor oil may be either petroleum-based or synthetic. The petroleum-based oils are more widely used than the synthetic oils and may be used in automotive engines, railroad and truck diesel engines, marine equipment, jet and other aircraft engines, and most small two- and four-stroke engines. 

Otto cycle—four-stroke engine cycle. See internal combustion engine. 

Pb was obtained as a solution of PbCl2. Tetra-ethyl lead was synthesised by a Grignard reaction and added to petrol together with ethylene dibromide. The petrol was burnt in a 50-cc four-stroke engine, and the exhaust passed into a wind tunnel (Fig. 7.8). The airflow in the tunnel gave sufficient dilution to limit the concentration of CO to 1000... 

Historically, the two-stroke engine has been a dominant force in the world of motorcycling and portable equipment due to its high power-to-weight ratio, simplicity of construction and low cost compared to equivalent sized four-stroke engines. 

Whilst steps can be made to improve the two-stroke from an emission s standpoint, the four-stroke engine has become the dominant power unit for today s motorcycles. Two-strokes continue to be used in off-road/racing applications, small, <50 cc, scooters, boating and portable equipment. 

Table 17.1 Issues for lubricant formulations in a four-stroke engine... 

CG-4 1995, for severe duty, high-speed, four-stroke engines using fuel containing <0.5% sulphur. Required for 1994 emission standards, can replace CD, CE and CF-4 lubricants. 

CH-4 1998, for high-speed, four-stroke engines designed to meet 1998 emission standards. Specifically formulated for fuel containing up to 0.5% sulphur w/w. Can replace CD, CE, CF-4 and CG-4 lubricants. 

The advantage of this treatment is that the total mol numbers are constant. We can then easily deal this reaction as a chemodynamic cycle. If in a combustion process the mol numbers are changing, then it is more advantageous to use the masses instead of the mol numbers. In the view of a chemodynamic cycle a combustion engine is still a four-stroke engine, but the meaning of the individual processes is different in comparison to those what a technician would explain ... 

Only the four-stroke engines will be discussed. 

The theoretical cycle of a four-stroke engine involves the following steps (Figure 3b). 

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