Engine Selection And Application

The internal combustion engine is used extensively as a driver for centrifugal and displacement pumps. Depending on the application, the engine fuel may be gasoline, natural gas, liquid petroleum gas (LPG), sewage gas, or diesel fuel. It may be either liquid-or air-cooled.

Basic Design Variations The basic design of the engine may vary. The cylinder block construction is vertical or horizontal, in-line or V-type. The number of cylinders ranges from 1 to 20. The engine cycle is either four (one power stroke in two revolutions of the crankshaft) or two (one power stroke in one revolution of the crankshaft). The combustion chamber and cylinder head design are classed as L-head (valves in the cylinder block) or valve-in head. In the diesel engine, the combustion chamber may be of the precombustion chamber design, where an ante chamber is used to initiate combustion, or of the direct injection design, where the fuel is injected directly into the cylinder. The piston design action may be vertical, horizontal, at an angle as in the V-type engine, or opposed piston (two pistons operating in the same cylinder).

Power Ratings The power range of engines in current production, depending on displacement, number of cylinders, and speed, is as follows:

1. Air-cooled gasoline, natural gas, and diesel: 1.0 to 75 hp (0.75 to 56 kW)

2. Liquid-cooled gasoline: 10 to 300 hp (75 to 224 kW)

3. Liquid-cooled natural gas, LPG, and sewage gas: 10 to 15,000 hp (75 to 11,200 kW)

4. Liquid-cooled diesel: 10 to 50,000 hp (75 to 37,300 kW)

5. Dual fuel, natural gas, LPG, and diesel: 150 to 25,000 hp (112 to 18,700 kW)

FIGURE 1 Natural gas engine driving a horizontal water pump for Winnipeg, Canada, water utility (Waukesha Motor)
FIGURE 2 Diesel engine driving pumps for flood-control station in Seattle (Waukesha Motor)

Typical engine driver applications are represented in Figures 1 and 2.

The rating of the internal combustion engine is the most important consideration in making the proper selection. The general practice is to rate engines according to the severity of the duty to be performed. The most common rating classifications are maximum, standby or intermittent, and continuous.

The maximum output is based on dynamometer tests that are corrected to standard atmospheric conditions for temperature and barometric pressure. In applications, this power rating is reduced by accessories such as cooling fans, air cleaners, and starting systems.

Standby, or intermittent, and continuous ratings are arrived at by applying a percentage factor to the net maximum power rating. For example, 75 to 80% is used for continuous and 90% for intermittent.

Duty cycle is a term used to describe the load pattern imposed on the engine. If the load factor (ratio of average load to maximum capabilities) is low, we call the duty cycle "light," but if it is high, we classify the cycle "heavy." Continuous, or heavy-duty, service is generally considered to be 24 h/day, with little variation in load or speed. Intermittent service is classified as duty where an engine is called upon to operate in emergencies or at reduced loads at frequent intervals.

In analyzing power problems when selecting a proper engine, certain terms are used in the industry:

displacement The displacement in cubic inches (cubic centimeters) of an engine cylinder is In USCS units, D = bore (in2) X 0.7854 X stroke (in) X no. of cylinders In SI units D = bore (cm2) X 0.7854 X stroke (cm) X no. of cylinders

Torque The twisting effort of the engine in pound-feet (Newton-meters) is bhp

rpm bkW

rpm engine power This is a measure of the theoretical characteristics of an engine. Brake horsepower (bkw) is the measurable power after the deduction for frictional losses:

5252 rpm 9545

brake mean effective pressure The average cylinder pressure to give a resultant torque at the flywheel in pounds per square inch (kilopascals)

792,000 X bhp

In USCS units bmep =-XD-(four-cycle)

In SI units bmep = 120 X 10xXD'kW (four-cycle)

piston speed At a given speed, the average velocity of piston in feet per minute (centimeters per minute) is rpm

In USCS units Piston speed = stroke (in) X 2 X 12

In SI units Piston speed = stroke (cm) X 2 X ~qqqq

In selecting an engine for a particular application, the following variables should be considered:

• Ambient air temperature

• Rotation and speed

• Bmep and piston speed

• Maintenance

• Operating atmosphere (dust and dirt)

• Vibrations and torsionals

• Engine pollutants

The observed power is that produced by an engine at the existing altitude and temperature. All engine manufacturers publish power ratings corrected to certain conditions; for conditions other than these, it is necessary to correct by applying a percentage factor for altitude and temperature. Generally this is 3^% per thousand feet (305 m) above sea level and 1% for every 10°F (5.6°C) above 60°F (50.4°C). In a turbocharged engine, there is no established standard and the engine manufacturer should be consulted.

The basic rotation of engines in current production is counterclockwise when viewed from the flywheel end of the engine, although many of the larger engines are available in both counterclockwise and clockwise rotation. The speed of the engine is generally fixed by the equipment being driven. Through the use of speed-increasing or -reducing gear boxes, the proper engine for a given application may be selected. A gear box may also be used to correct a rotation problem.

Speed ranges for engines generally fall into three categories:

High-speed engines generally offer weight and size advantages as well as cost savings and thus are used for standby applications. On the other hand, medium- or low-speed engines, although heavier and larger, offer a gain in service life and lower maintenance costs.

The speed flexibility of an engine drive is important when the engine is to be used to drive a pump that must move variable quantities of liquid. The engine speed may be changed very simply either manually or through the use of liquid or pressure controls.

Bmep is generally a measure of load, and piston speed a measure of potential wear and maintenance. Although the introduction of the turbocharged and intercooled engine has somewhat changed the consideration given these factors, it is still important to consider them in selecting engines where long life is a factor.

Maintenance of engines has been considered by some as objectionable and more costly than electric power. A recent innovation of engine manufacturers, in the form of a service contract for installations where trained personnel are not available or desirable for economic reasons, can eliminate these objections and costs. The complete maintenance of the engine is done on a fixed-fee basis for a designated period of time.

The exhaust gases of spark ignition and compression ignition (diesel) engines contain pollutants that for many engine applications are increasingly the subject of legislation restricting the quantity of pollutants the engine can emit. Examples of pollutants are carbon monoxide (CO), oxides of nitrogen (NOx), unburned hydrocarbons (HC), and, for diesels, particulates in the form of carbon soot. Pollutants can be measured on a specific basis, such as g/bhp-hr and ppm (parts per millions by volume), or on a site basis, such as lb/hr or tons/year. Engine manufacturers are designing "clean" engines that incorporate features to minimize the formation of pollutants during combustion and may include catalytic converters and particulate fibers in the exhaust system to further reduce the pollutants emitted in the exhaust gases.

The remaining conditions listed previously will be discussed in detail later.

Survival Treasure

Survival Treasure

This is a collection of 3 guides all about survival. Within this collection you find the following titles: Outdoor Survival Skills, Survival Basics and The Wilderness Survival Guide.

Get My Free Ebook


Post a comment