Piston-Engine Based Power Plants
Muhammad Hanif Sarwar
The Bulk of material in these slide slides from Paul Breeze, Power Generation Technologies , Elsevier, 2005.
EE-415: Power Generation, Transmission and Distribution, Spring 2013
Same technology used
today in oil wells
The Lift Pump
First true steam engine by Thomas Newcomen (blacksmith) developed in 1712
First modern steam engine: James Watt, 1769 (patent), 1774 (prod.)
Double-action steam engine:
stops to take on
water and fuel.
Piston engines or reciprocating engines are used throughout the world
in applications ranging from lawn mowers to cars, locomotives, ships
trucks, and for power and combined heat and power generation.
Engines vary in size from less than 1 kW to 65,000kW.
They can burn a wide range of fuels including natural gas, biogas,
LPG, gasoline, diesel, biodiesel, heavy fuel oil and even coal.
Used for standby power or for combined heat, and power in homes and
Usually cheap because they are mass produced
Relatively low efficiencies
Larger standby units
Used where supply of power is critical; in hospitals or to support highly
sensitive computer installations such as air traffic control
Many commercial and industrial facilities use medium-sized piston engine-
based combined heat and power units for base-load power generation.
Can be used for base-load, grid-connected power generation
Smaller units provide electricity to isolated communities
Larger engines tend to be more expensive
Large, megawatt scale engines are the most efficient prime movers
available,with simple cycle efficiencies approaching 50%.
Working Principal of a Piston Engine
In its most basic form, the piston engine comprises a cylinder
sealed at one end and open at the other end.
A disc or piston which fits closely within the cylinder is used to
seal the open end and this piston can move backwards and
forwards within the cylinder.
This it does in response to the expansion and contraction of the
gas contained within the cylinder.
The outside of the piston is attached via a hinged lever to a
crankshaft. Movement of the piston in and out of the cylinder
causes the crankshaft to rotate and this rotation is used to derive
motive energy from the piston engine.
Working Principal of a Piston Engines
Reciprocating or Internal Combustion Engine
Types of Piston Engines
Reciprocating or internal combustion engines
Spark Ignition type
Compression or diesel type: High efficiency for power generation
applications but produces high level of atmospheric pollution
particularly nitrogen oxide
Valves are employed to admit a mixture of fuel and air into the sealed
piston chamber where it is burnt to generate energy.
External Combustion Engines or Stirling Engine
Developed for specialized power generation
Heat energy used to drive it is applied outside the sealed piston
Piston Engine Types
Internal Combustion(IC) Engines
Spark Ignition Type
The Otto cycle engine employs a spark to ignite a mixture of air and
fuel compressed by the piston within the cylinder.
Explosive release of heat energy increases the gas pressure in the
cylinder, forcing the piston outwards as the gas expands.
This explosion force on the piston turns the crankshaft
Compression Type Engines
The Otto cycle was modified by Rudolph Diesel in the 1890s.
Air is compressed by a piston to such a high pressure that its
temperature rises above the ignition point of the fuel which is then
introduced to the chamber and ignites spontaneously without spark.
A further subdivision depends on whether the engine utilises a
two- or a four-stroke cycle.
The former is attractive in very small engines as it can provide relatively
high power for low weight.
For power generation, some very large engines also use a two-stroke
Most small- and medium-sized engines for power generation employ the
IC Engine Types
Either air (diesel cycle) or a fuel and air mixture (Otto cycle) is drawn
into the piston chamber
The gases in the cylinder are compressed
In the case of the Otto cycle, a spark ignites the fuel–air mixture at the
top of the piston movement creating an explosive expansion of the
compressed mixture which forces the piston down again.
In the diesel cycle, fuel is introduced close to the top of the compression
stroke, igniting spontaneously with the same effect.
Exhaust gases are forced out of the piston chamber. In either case a
large flywheel attached to the crankshaft stores angular momentum
generated by the power stroke and this provides sufficient momentum
to carry the crankshaft and piston through the three other strokes
required for each cycle.
The introduction of fuel and air, and the
removal of exhaust is controlled by valves
which are mechanically timed to coincide
with the various stages of the cycle.
Intake and exhaust strokes are not separate. Instead fuel is forced
into the piston chamber (intake) towards the end of the power
stroke, pushing out exhaust gases through a valve at the top of the
chamber. A compression stroke is then followed by ignition of fuel
and a repeat of the cycle.
Simpler and cheaper
Each stroke is power stroke
Smoother power in one-
Some unburned fuel escapes
Three categories of engines : high-, medium-, and low-speed
High-speed engines are the smallest and operate up to 3600 rpm.
The largest slow-speed engines may run as slow as 58 rpm.
Engine performance varies with speed. High-speed engines provide
the greatest power output as a function of cylinder size.
Engine Size and Speed
However the larger, slower engines are more efficient and last
longer. Thus the choice of engine will depend very much on
the application for which it is intended.
Large, slow- or medium-speed engines are generally more
suited to base-load generation but it may be more cost effective
to employ high-speed engines for back-up service where the
engines will not be required to operate for many hours each
In addition to standby service or continuous output base-load
operation, piston engine power plants are good at load
Engine Size and Speed
Spark Ignition Engines
They can burn a variety of fuels including gasoline, propane and
landfill gas but the most common fuel for power generation
applications is natural gas.
Most are four-stroke engines available in sizes up to around 6.5MW.
With natural gas, the engine efficiency varies between 28% for smaller
engines and 42% for larger engines.
An engine tuned for maximum efficiency will produce roughly twice
as much nitrogen oxides as an engine tuned for low emissions.
Many natural gas engines are derived from diesel engines with 60–
80% of the output of the original diesel.
More expensive than diesel engines but longer life and lower-
maintenance costs. Higher power can be achieved with a dual-fuel
Dual Fuel Engines
Natural gas–air mixture is admitted to the cylinder during the intake
stroke, then compressed during the compression stroke.
At the top of the compression stroke the pilot diesel fuel is admitted
and ignites spontaneously, igniting the gas–air mixture to create the
Engine operates at close to the conditions of a diesel engine, with a
high-power output and high efficiency, yet with the emissions close to
those of a gas-fired spark-ignition engine.
Dual fuel engines operate with between 1% and 15% diesel fuel.
A dual fuel engine can also burn 100% diesel if necessary, with much
Heat energy used to drive a Stirling engine is applied outside the
cylinders which are completely sealed.
Stirling engines often use helium or Hydrogen within cylinders.
A normal Stirling engine has two cylinders, an expansion cylinder
and a compression cylinder. The two are linked and heat is applied
to the expansion cylinder while the compression cylinder is cooled.
Careful balancing of the system allows the heat energy to be
converted into rotational motion.
Advantages: As heat energy is applied externally, hence in theory,
be derived from any heat source.
Stirling engines have been used to exploit solar energy and for
biomass applications. However their use is not widespread.
Typical engines sizes in use and development range from 1 to
The efficiency of piston-engine-based power generation varies from
25% for small engines to close to 50% for the very largest engines.
Between 50% and 75% of energy can be converted into combined heat
and power (CHP) systems.
Between 30% and 50% of energy in exhaust gases can be used to
generate medium-pressure steam or can be used to generate hot water.
The main engine case cooling system can capture up to 30% of the
total energy input which could be passed through a heat exchanger to
provide a source of hot water, although in some cases it can be used to
produce low-pressure steam as well.
In the USA in 2000, there were 1055 engine-based CHP systems in
operation with an aggregate generating capacity of 800MW
Cooling of a Diesel Engine
Air cooling used in small and
portable engines through fins.
In natural circulation systems,
water circulates due to
difference in density at
Standby diesel power plants
up to 200 kVA use forced
circulation cooling system
In bigger plants, hot water is
cooled in a cooling tower and
re-circulated again. Make-up
water is therefore needed. Forced Circulation Cooling System.
Diesel Power Stations
The design and layout of the plant are quite simple.
It occupies less space as the number and size of the auxiliaries is small.
It can be located at any place.
It can be started quickly and can pick up load in a short time.
There are no standby losses.
It requires less quantity of water for cooling.
The overall cost is much less than that of steam power station of the same
The thermal efficiency of the plant is higher than that of a steam power
It requires less operating staff.
Diesel Power Stations
The plant has high running charges as the fuel (i.e., diesel) used is costly.
The plant does not work satisfactorily under overload conditions for a
The plant can only generate small power.
The cost of lubrication is generally high.
The maintenance charges are generally high.