Diesel Engine for Power Generation
by Starlight Generator dieselgeneratortechDiesel engines have
historically been the most common type of reciprocating engine for both small
and large power generation applications. However, in the United States and
other industrialized nations, diesel engines are increasingly restricted to emergency
standby or limited duty-cycle service because of air emission concerns and also
because of the high cost of fuel. Consequently, the natural gas-fueled SI engine
is now the engine of choice for the higher duty cycle stationary power market
(over 500 hr/yr) and is the primary focus of this report.
Compression ignition diesel
engines are among the most efficient simple-cycle power generation options on
the market. Efficiency levels increase with engine size and range from about 30
percent (HHV) for small high-speed diesels up to 42 to 48 percent (HHV) for the
large bore, slow speed engines.
High speed diesel
engines (>=1,000 rpm) are available for up to about 4 MW in size. Low speed
diesel engines (60 to 275 rpm) are available as large as 80 MW. Medium speed
diesel engines (400 – 1000 rpm) are available for up to approximately 17 MW.
Diesel engines typically
require compression ratios of 12:1 to 17:1 to heat the cylinder air to a temperature
at which the injected fuel will ignite. The quality of fuel injection
significantly affects diesel engine operating characteristics, fuel efficiency,
and emissions. Fine atomization and good fuel dispersion by the injectors are
essential for rapid ignition, ideal combustion and emissions control.
Manufacturers are increasingly
moving toward electronically controlled, high pressure injection systems that
provide more precise calibration of fuel delivery and accurate injection
timing.
Depending on the engine
and fuel quality, diesel engines produce 5 to 20 times the NOx (on a ppmv basis)
of a lean burn natural gas engine. Diesel engines on marine engines often emit
over 20 lbs NOx/MWh and present on road engines emit less than 13 lbs NOx/MWh.
New diesel engines will achieve rates of approximately 0.65 lb NOx/MWh. Diesel
engines also produce assorted heavy hydrocarbons and particulate emissions.
However, diesel engines produce significantly less CO than lean burn gas
engines.
The NOx emissions from
diesels burning heavy oil are typically 25 to 30 percent higher than diesels
using distillate oil. Common NOx control techniques include delayed fuel
injection, exhaust gas recirculation, water injection, fuel-water
emulsification, inlet air cooling, intake air humidification, and compression ratio
and/or turbocharger modifications. In addition, an increasing number of larger
diesel engines are equipped with selective catalytic reduction and oxidation
catalyst systems for post-combustion emissions reduction.
High speed diesel
engines generally require high quality fuel oil with good combustion
properties. No. 1 and No. 2 distillate oil comprise the standard diesel fuels.
Ultra-low sulfur diesel with sulfur contents of less than 0.15 ppm is now
required for the new Tier 4 diesel engines to reduce sulfur emissions. High speed
diesel engines are not suited to burning oil heavier than distillate. Heavy
fuel oil requires more time for combustion and the combination of high speed
and contaminants in lower quality heavy oils cause excessive wear in high speed
diesel engines. Many medium and low speed diesel designs burn heavier oils
including low grade residual oils or Bunker C oils.
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Created on Apr 21st 2019 22:28. Viewed 292 times.