Chapter 3: Engine Operation

What is the relationship between stroke in an engine and torque?

An engine with a longer stroke produces more torque than an engine with a shorter stroke having the same displacement.

How does altitude affect horsepower?

Higher altitudes have less oxygen in the air, which results in a smaller charge inside the cylinder.

What is the purpose of glow plugs in a diesel engine?

Glow plugs are used to preheat air inside the combustion chamber to facilitate ignition of the charge.

What is the sump in an engine?

The sump is a removable part of the engine crankcase that serves as an oil reservoir and provides access to internal parts. It provides a bearing surface for vertical shaft engines and forms the lower section of the engine.

What is the bore and stroke of an engine?

The bore of an engine is the diameter of the cylinder bore, whereas the stroke of an engine is the linear distance that a piston travels in the cylinder bore from top dead center (TDC) to bottom dead center (BDC).

What is the bearing journal on the crankshaft of an engine?

A bearing journal is a precision ground surface within which the crankshaft rotates. They mate with bearing surfaces in the cylinder block.

What is cetane number in diesel fuels?

A cetane number is the measurement of how easily diesel fuel will ignite. The numbers range from a low of 33 to a high of 64.

What are the three valve systems in two cycle engines?

(1) A reed valve valving system uses a valve made from thin spring steel that opens and closes with pressure changes in the crankcase to control air-fuel mixture flow. (2) A three-port valving system uses three ports to control the flow of air-fuel mixture and exhaust gas. (3) A rotary valve valving system uses a rotating flat disk with a section removed to control air-fuel mixture flow.

What are four ways to measure horsepower in engines?

(1) Water (2) Electric (3) Eddy (4) Prony brake

Describe the terms tappet, cam lobe, rocker arm, valve guide.

-A tappet is an engine component that rides on the camshaft and pushes the bottom of the valve stem to open the valve. -A cam lobe is an egg-shaped protrusion on the camshaft that moves a tappet to open a valve. -A rocker arm is an engine component that acts as a pivoting device for opening and closing overhead valves. -A valve guide is an engine component that aligns a valve stem in a linear path. It allows rotation of the valve during the opening and closing to increase valve life.

What are two advantages and two disadvantages of two cycle engines?

-Advantages: (1) fewer moving parts (2) less weight for comparable output -Disadvantages: (1) more noise (2) greater exhaust emissions

How are friction and antifriction bearings different?

-Friction bearing: consists of a fixed, non-moving bearing surface, commonly uses lubricating oil to separate the moving component from the mated non-moving bearing surface, and commonly consists of material that is softer than the supported component -Antifriction bearing: contains moving elements, commonly made with hardened rolling elements (balls and rollers), and reduces lubrication requirements while decreasing starting and operating friction

What are the three piston rings?

-The compression ring is the piston ring located in the ring groove closest to the piston head. It seals the combustion chamber from any leakage during the combustion process. -The wiper/scraper ring is the piston ring with a tapered face located in the ring groove between the compression ring and the oil ring. It's used to further seal the combustion chamber and to wipe the cylinder wall clean of excess oil. -The oil ring is the piston ring located in the ring groove closest to the crankcase. It's used to wipe excess oil from the cylinder wall during piston movement.

What does the flywheel do in a small engine? Diesel engines?

-The flywheel supplies the inertia required to prevent loss of engine speed and possible stoppage of crankshaft rotation between combustion intervals. The inertia of the flywheel provides a dampening effect on the engine as a whole to even out radical acceleration forces and rpm deviations produced in the engine. -A diesel engine doesn't have a magnet because it doesn't need the spark.

What is brake horsepower?

Brake horsepower (BHP), also known as shaft horsepower, is the amount of usable power taken from an engine. It's the amount of power possible, including any loss from internal friction.

What is the formula for the displacement of an engine?

D = 0.7854 x B^2 x S (1) D = displacement (in cu in.) (2) 0.7854 = constant (3) B^2 = bore squared (in in.) (4) S = stroke (in in.)

What does the injection pump do in a diesel engine?

The injection pump is a component that provides pressurized fuel to the cylinder at precise intervals.

What is turbocharging in a diesel engine and what is the purpose?

Turbocharging is the process of using a compressor to raise the pressure and the density of the air entering an engine. This is done to increase the total mass of air introduced per cycle.

What is valve overlap?

Valve overlap is the period during engine operation when both intake and exhaust valves are open at the same time.