Manufacturers use engine, ignition, and fuel modifications to achieve federally mandated standards. Briefly discuss two common modifications.

Question

What will be an ideal response?

Answer 1

- A cool area of fuel remains unburned along all cool surface areas in the combustion chamber and cylinder. The amount of exposed area is referred to as the surface-to-volume ratio. Engines have as little exposed surface area as possible on the combustion chamber and the top of the piston. Engine designers have moved top piston rings as close to the top of the piston as possible to avoid having much surface area on the piston exposed to flame.
- Engines have higher cooling system temperatures to improve thermal efficiency. Newer engines operate at 1900F to 2180F; older engines ran at 1600F to 1800F.
- Advancing ignition timing increases HC and NOX, but if done correctly, it can increase fuel economy as well. More efficient use of fuel helps reduce overall emissions. Using the knock sensor, the computer provides the best spark advance for the condition at hand.
- Changing the camshaft design specifications can alter emissions, especially at idle. This is done with variable valve timing, often making an EGR valve unnecessary. Increasing valve overlap increases HC emissions but lowers NOX emissions at low engine rpm.