Internal Combustion Engines –The Diesel

References

Required•Principles of Naval Engineering–(pP. 80-97)

Optional•Introduction to Naval Engineering–(Ch 11)

Objectives

A. Know the advantages, disadvantages, and capabilities of diesel engines in propulsion plants.

B. Comprehend the basic operation, key components, and safety considerations of diesel engines and propulsion plants.

C. Know the features of the diesel fuel systems and how it functions with respect to the safe operation of the engine.

The Diesel is a Hacker

Engine Uses

Harpers Ferry (LSD 49)

LCU

USS Oriole (MHC 55)

Emergency Power Generators

Structural Components

• Cylinder Block– Part of engine frame

that contains cylinders in which piston moves

– Supports liners & head

Structural Components

• Cylinder Head/Assembly– Serves to admit, confine, and release fuel/air– Cover to cylinder block– Supports valve train

• Crankcase– Engine frame section that houses the

crankshaft• Oil sump– Reservoir for collecting and holding lube oil

Moving Components

• Three Groups – according to motion– Reciprocating only (pistons and valves)– Reciprocation & rotary (connecting rods)– Rotary only (crankshafts and camshafts)

Moving Components• Piston– Acted on by combustion gases– Lightweight but strong/durable

• Piston Rings– Transfer heat from piston to

cylinder– Seal cylinder & distribute lube oil

• Piston Pin– Pivot point connecting piston to

connecting rod• Connecting Rod– Connects piston & crankshaft– reciprocating rotating motion

Moving Components• Crankshaft– Combines

work done by each piston

– Drives camshafts, generator, pumps, etc.

Moving Components• Flywheel– Absorbs and

releases kinetic energy of piston strokes -> smoothes rotation of crankshaft

Moving Components

• Valves– Intake: open to admit air to

cylinder (with fuel in Otto cycle)– Exhaust: open to allow gases to

be rejected

• Camshaft & Cams– Used to time the addition of

intake and exhaust valves– Operates valves via pushrods &

rocker arms

Operation

• Increased pressure of combustion gases acts on piston -> converted to rotary motion

• Can be 2 or 4 stroke engines– 2-stroke: 1 power stroke per 1 crankshaft rev– 4-stroke: 1 power stroke per 2 crankshaft rev

Operation• Engine stroke– A stroke is a single traverse of the cylinder by

the piston (from TDC to BDC)– 1 revolution of crankshaft = 2 strokes of piston

Four-Stroke Diesel Engine

• Intake stroke– Intake valve open, exhaust valve shut– Piston travels from TDC to BDC– Air drawn in

• Compression stroke– Intake and exhaust valves shut– Piston travels from BDC to TDC– Temperature and pressure of air increasehttp://www.myrctoys.com/engines/engine.swf

Four-Stroke Diesel Engine

• Power stroke– Intake and exhaust valves shut– Fuel injected into cylinder and ignites– Piston forced from TDC to BDC

• Exhaust stroke– Intake valve shut, exhaust valve open– Piston moves from BDC to TDC– Combustion gases expelled

Two-Stroke Diesel Engine• 1 power stroke every crankshaft revolution (vice every two w/

4-stroke)• Uses pressurized air to simultaneously supply new air and

expel combustion gases• Scavenging– Exhaust valve open, inlet port exposed– Pressurized air enters, expels combustion gases– Piston near BDC

Two-Stroke Diesel Engine

• Compression– Intake and exhaust valves shut– Piston travels from BDC to TDC– Temperature and pressure of air increase

• Power stroke– Intake and exhaust valves shut– Fuel injected into cylinder and ignites– Piston forced from TDC to BDC

Two vs. Four-Stroke Engines

• Two-stroke advantages– Higher power to weight ratio– Less complicated valve train

• Four-stroke advantages– More efficient burning process– As size increases, power-to-weight ratio

improves

Gasoline vs. Diesel Engine

Supporting Systems

• Air system– Supplies & removes air/gases– Air supplied at constant pressure by

blower/compressor• Fuel System– Carburetor: mixes air & fuel in proper proportion

(NOT on diesels)– Fuel injector: sprays fuel in (more efficient)

Supporting Systems

• Ignition system– Diesel has compression ignition– Gasoline has spark plugs

• Cooling system– Uses fresh water and/or salt water to cool

• Lubrication system– Provide lubrication and cooling

Take Aways

• Draw a P-V diagram for a gas engine and diesel engine and explain the Otto cycle. Label the thermodynamic processes.

• Describe the major differences between a two stroke and four stroke engine. Give advantages and disadvantages of each.

• Describe a 4 stroke engine operation through one complete revolution of the crank shaft

• Discuss the necessity for starting air in a diesel engine

Questions?