Turbine is driven, engine drives. in reality nothing, both use steam pressure to create a desired output. Motion, turbine has 1 moving part that spins on its axis. Engine has many moving parts spinning an axis (crankshaft).
A turbine operates in a way similar to either a jet engine, or an old water-wheel. In either case, a steam turbine converts the thermal energy of the steam to rotary mechanical energy much more efficiently.
In engine, wet steam may also be used while in steam turbine, steam should be in superheated condition.
Power output or steam to power ratio is comparatively very high in steam turbine as losses (e.g frictional, velocity etc) are very less. So, plant efficiency is much higher.
With the high cost of the fuel used for internal combustion engines, the rebirth of steam engines is visible at present. Steam engines are very good in recapturing the waste energy from many sources including steam turbines exhaust. The waste heat from steam turbine is used in combined cycle power plants. It further allows discharging the waste steam as exhaust in much low temperatures
Maintenance problems are more in steam engine than turbine due to its reciprocating motion. steam engines are of old class of machines which are now not in used widely.
The turbine uses steam at higher pressures and in my view less efficiently than a closed piston power source does. Lower pressures can be used in the closed piston type engine and levels of output can be changed by simply adding more cylinders or expanding the diameter of the piston, there are more moving parts than a turbine.
A turbine is most fuel efficient in situations where full power is used most often, such as a power plant, where the turbine spins a generator.
An engine is most efficient in low-speed, high torque applications, such as a piston set coupled to the drive wheels of an old steam locomotive.
The main difference between steam turbine & steam engine is, turbine is rotating equipment while most of the steam engines are of reciprocating type.
For small systems, the steam engine is preferred to steam turbines since the efficiency of turbines depend on the steam quality and the high speed. The exhaust of the steam turbines is at very high temperature and thus, low thermal efficiency too.
Being very high quality of materials to be used for construction of various parts of steam turbine, it is very much costly compared to steam turbine.
Great quantity of power generation can be achieved by very large are steam turbine which is not the case with engines.
While, steam engine and steam turbine use the large latent heat of vaporization of steam for the power, the main difference is the maximum revolution per minute of the power cycles that both could provide. There is a limit for the number of cycles per minute that could provide with a steam driven reciprocating piston, inherent in its design.
Steam engines in locomotives, normally have double acting pistons run with steam accumulated at both faces alternatively. The piston is supported with piston rod connected with a cross head. Cross head is further attached to the valve control rod by a linkage. The valves are for supply of the steam, as well as, for exhausting the used steam. The engine power generated with the reciprocating piston is converted to a rotary motion and transferred to the drive rods and the coupling rods that drive the wheels.
The modern technology used for steam flow direction and flow pattern is more sophisticated compared to the old technology of peripheral flow. The introduction of direct hit of steam with blades at an angle that produces a little or almost no back resistant gives the maximum energy of the steam to the rotary movement of the turbine blades.
The disadvantages of the turbines are: small turndown ratios, which are the degradation of performance with the reduction of steam pressure or flow rates, slow start up times, which is to avoid thermal shocks in thin steel blades, large capital cost, and the high quality of steam demanding feed water treatment.
The main disadvantage of steam engine is its limitation of the speed and the low efficiency. Normal steam engine efficiency is around 10 – 15 % and newest engines are capable of operating at much higher efficiency, around 35% with the introduction of compact steam generators and by keeping the engine in an oil free condition thus, increasing the fluid life.