2. 8
Fuel Supply, Air Induction, and Emissions

3. Learning Objectives
Name various types of fuel that can be used in a small engine and list practical applications for each.
Explain the importance of proper fuel-oil mixture in a two-cycle engine.
Describe the purpose of fuel filters.
Explain fuel pump operation.
Describe the operation of a pressurized fuel system.
Describe the purpose of an air cleaner.
Explain the importance of emission control.

4. Engine Fuels Gasoline Liquefied petroleum gas Natural gas Kerosene
High power potential
Widely available
Liquefied petroleum gas
Natural gas
Kerosene
Diesel fuel

5. Gasoline Most popular fuel for small engines Refined from petroleum
Desirable characteristics
Ignites readily, burns cleanly, resists detonation
Vaporizes easily
Free of dirt, water, and abrasives

6. Octane Number Ability to resist detonation Premium grade burns slower
Used in high-compression engines
Regular grade burns faster
Used in most small engines

7. Unleaded Gasoline Leaded gasoline phased out in 1980s
Damaged catalytic converters
Oxygenates added to increase octane
Super unleaded or premium unleaded
Increases moisture absorption
Can cause corrosion and damage plastic

8. Fuel Stabilizers Added to fuel for storage Keep fuel fresh
Reduce chemical breakdown
Less gum and varnish
Contain petroleum distillate

9. Two-Cycle Fuel Mixtures
Oil mixed with gas
Ratio varies with engine design
Too little oil
Overheating
Scoring of internal components
Too much oil
Incomplete combustion
Carbon buildup

10. Liquefied Petroleum Gas and Natural Gas
Require special fuel system
Liquefied petroleum gas (LPG)
May consist of propane, butane, or mix
Burns cleanly with high anti-knock rating
No loss of horsepower
Natural gas
20% loss of horsepower

11. Combustion of LPG Ignition timing advanced
Burns slower than gasoline
Higher ignition temperature
May require higher voltage at spark plug
Colder plugs are smaller plug gaps

12. LPG vs. Gasoline Advantages of LPG Disadvantages of LPG Cheaper
Less engine wear and maintenance
Produces smoother power with fewer emissions
Disadvantages of LPG
High initial equipment costs
Less availability
Harder to start in cold weather

13. Typical LPG Fuel System
(Clinton Engine Corp.)

14. Kerosene and Diesel Fuels
Some gas engines can be converted
Low compression head and special carburetor
Started and warmed on gasoline
Switched to fuel oil or kerosene when warm
True diesel engines use diesel fuel
Fuel injected into cylinder
High compression ratio (up to 20:1)

15. Fuel Systems All parts that help deliver fuel to cylinder Fuel tank
Fuel line
Fuel filter
Carburetor
Fuel pump

16. Fuel Tanks Fuel filler caps Strainers Tanks may have fuel pick-up line
Vented
Prevent debris from entering tank
Strainers
Capture debris during refueling
Tanks may have fuel pick-up line
Weighted to keep pick-up in fuel

17. Fuel Lines Route fuel from tank to carburetor Typically flexible hoses
Special material and design
Reduce emissions
Withstand constant exposure to fuel
Fastened to fittings with hose clamps

18. Fuel Line Connection

19. Low Permeation Fuel Tanks and Lines
Reduce evaporative emissions
Must be replaced with same type
Compliance with emission standards

20. Fuel Filters Filter screens Replaceable inline filter Pickup tube
Tank fitting
Replaceable inline filter
Installed between tank and carburetor
Unidirectional

21. Inline Fuel Filter

22. Fuel Pumps Installed between tank and carburetor
Provide pressurized fuel flow
Tank lower than carburetor
Tank considerable distance from carburetor
Engine is used in different positions
Mechanical and impulse diaphragm types

23. Mechanical Fuel Pumps Rocker arm follows eccentric
Pull rod compresses spring and pulls down diaphragm
Diaphragm creates vacuum to draw in fuel
Check valves at outlet prevents backflow
Spring pressure returns diaphragm
Forces fuel out of chamber
Check valve at inlet prevents backflow

24. Mechanical Fuel Pump Operation

25. Impulse Diaphragm Fuel Pumps
Operated by vacuum
4-cycle use manifold vacuum
2-cycle use crankcase vacuum
May be built into carburetor

26. Impulse Diaphragm Fuel Pump Operation
Vacuum pulse moves diaphragm
Draws fuel into chamber
Compresses return spring
Vacuum decreases
Spring pressure returns diaphragm
Pushes fuel out of pump
Check valves prevent backflow

27. Pressurized Fuel System
Used with outboard motors
Tank far below carburetor
Crankcase gases pressurize fuel tank
Initial pressure provided by hand pump
Pressure forces fuel up pick-up tube

28. Vapor Return Fuel Systems
Vapor in carburetor disrupt fuel flow
Engine will not run until vapor condenses
System returns vapor to tank
Prevents vapor lock

29. Air Induction Systems Delivers air to carburetor Components
Filter and housing
Intake plenum

30. Air Cleaners and Air Filters
Remove dust from air
Dust causes engine wear
Three common types
Oil-wetted
Dry
Dual-element
Clogged filter causes engine to run rich

31. Oil-Wetted Air Cleaners
Made from polyurethane foam
Pores in foam trap particles
Filter should be cleaned regularly
Every 25 hours of operation (or once a season)
Washed with soap and water
Wetted with oil

32. Dry-Type Air Cleaners Thrown away when dirty
Never clean with compressed air
Pleated paper, felt, fiber, or flocked screen
Cylindrical or rectangular
Pleats in paper increase surface area
Flexible gasket creates seal

33. Dry-Type Filter Element

34. Pleated Paper Filter Cartridge

35. Dual-Element Air Cleaners
Extra protection in dusty conditions
Foam pre-cleaner
Some oiled; some dry
Cleaned like foam air cleaner
Pleated paper cartridge
Replaced when dirty

36. Typical Dual-Element Air Cleaner

37. Crankcase Breathers Prevent pressure buildup in crankcase
Reed valves vent pressure
In old engines, vented to atmosphere
New engines vent to air filter or carburetor
On OHV engines, located in valve cover
On L-Head engines, located in crankcase
Doubles as valve cover

38. Crankcase Breather on L-Head Engine

39. Mufflers Function: Spark arrestor Deflectors and heat shields
Reduce exhaust noise
Redirect exhaust gas
Trap sparks
Produce correct back pressure
Spark arrestor
Deflectors and heat shields

40. Typical Mufflers

41. Emissions Mowing lawn ½ hr = driving 172 miles Exhaust gassesCO
NOX HC
Evaporative emissions

42. Emission Control Regulations
Clean Air Act
1990 amendment to CAA
California Air Resources Board (CARB)
Environment Protection Agency (EPA)
Engine must be properly tuned

43. Phase 1 Standards for Small Spark-Ignition Engines
Established in 1995 by EPA
Regulated engines 25 HP and up
Goal to reduce HC and NOX emissions 32%
5 displacement classes
2 handheld (2-cycle)
3 non-handheld (4-cycle)
2-cycle mowers excluded

44. Phase 2 Standards for Small Spark-Ignition Engines
Established 2000 by EPA
Goal to reduce NOX and HC emissions 70%
Phased in between 2002 and 2007
Larger engines switched to OHV design
Added two new handheld classes
66cc and under
66cc to 100cc

45. Phase 3 Emission Standards
Established 2007 by EPA
Goal to reduce HC, NOX, and CO emissions
Limits evaporative emissions
Phased in by 2012
Compliance may require new designs

46. Impact of Regulations on Technicians and Consumers
Must keep up-to-date with regulations
Repairs must keep engine in compliance
Model year determines applicable regulations
Consumers
Should perform regular maintenance
Should avoid fuel spillage

47. Information Sticker

48. What fuels might be used in various small gas engines
What fuels might be used in various small gas engines? Gasoline, liquefied petroleum gas, natural gas, kerosene, fuel oil, and diesel fuel.

49. What can happen if an improper fuel/oil mixture is used in a 2-cycle engine? Too little oil can result in overheating and scoring. Too much oil can result in incomplete combustion and carbon buildup.

50. What precaution must be taken when installing an inline fuel filter
What precaution must be taken when installing an inline fuel filter? The fuel filter must be installed so fuel flows through it in the right direction.

51. Describe how the fuel pump diaphragm works to pump fuel
Describe how the fuel pump diaphragm works to pump fuel. The diaphragm moves to increase volume in the pump, which draws in fuel. Spring pressure returns the diaphragm to its original position, forcing fuel out of the pump.

52. In a pressurized fuel system like that used with an outboard engine, what pressurizes the fuel tank? Crankcase pressure

53. What is the primary function of an air cleaner
What is the primary function of an air cleaner? It prevents particles in the air from entering the engine.

54. Why is it important for a technician to know when an engine was manufactured? The model year of the engine determines which EPA regulations apply to it.