![]() ![]() Loss due to condensation is restricted to the LP cylinder. There are other advantages: as the temperature range is smaller, cylinder condensation is reduced. The complete expansion of the steam occurs across multiple cylinders and, as there is less expansion in each cylinder, the steam cools less in each cylinder, making higher expansion ratios practical and increasing the efficiency of the engine. In the compound engine, high-pressure steam from the boiler first expands in a high-pressure (HP) cylinder and then enters one or more subsequent lower pressure (LP) cylinders. Compounding engines Ī solution to the dilemma was invented in 1804 by British engineer Arthur Woolf, who patented his Woolf high pressure compound engine in 1805. These irreversible heat flows decrease the efficiency of the process, so that beyond a certain point, further increasing the expansion ratio would actually decrease efficiency, in addition to decreasing the mean effective pressure and thus the power of the engine. ![]() However, in practice the material of the surrounding cylinder acts as a heat reservoir, cooling the steam in the earlier part of the expansion and heating it in the later part. Ideally, the steam would expand adiabatically, and the temperature would drop corresponding to the volume increase. Īn earlier cut-off increases the expansion ratio, which in principle allows more energy to be extracted and increases efficiency. This " cut-off" allows much more work to be extracted, since the expansion of the steam is doing additional work beyond that done by the steam at boiler pressure. After the steam supply is cut off the trapped steam continues to expand, pushing the piston to the end of its stroke, where the exhaust valve opens and expels the partially depleted steam to the atmosphere, or to a condenser. The steam pressure forces the piston down the cylinder, until the valve shuts (e.g. In a single-expansion (or 'simple') steam engine, the high-pressure steam enters the cylinder at boiler pressure through an inlet valve. There are many compound systems and configurations, but there are two basic types, according to how HP and LP piston strokes are phased and hence whether the HP exhaust is able to pass directly from HP to LP ( Woolf compounds) or whether pressure fluctuation necessitates an intermediate "buffer" space in the form of a steam chest or pipe known as a receiver ( receiver compounds). Around 1850, compound engines were first introduced into Lancashire textile mills. Invented in 1781, this technique was first employed on a Cornish beam engine in 1804. Multiple-expansion engines employ additional cylinders, of progressively lower pressure, to extract further energy from the steam. Ī typical arrangement for a compound engine is that the steam is first expanded in a high-pressure (HP) cylinder, then having given up heat and losing pressure, it exhausts directly into one or more larger-volume low-pressure (LP) cylinders. Small high-pressure cylinder (left) and large low-pressure cylinder (right)Ī compound steam engine unit is a type of steam engine where steam is expanded in two or more stages. High-pressure steam (red) passes through three stages, exhausting as low-pressure steam (blue) to the condenser Cutaway of triple expansion compound steam engine, 1888 Robey horizontal cross-compound steam engine For compound steam locomotives, see Compound locomotive.ĭouble-acting triple-expansion marine engine ![]()
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