practice exam 2 Flashcards
4 types of way to add fuel and where do they occur
(1) carbeurator, upstream, near intake manifold, common to all cylinders (2) throttle body, upstream, common to all cylinders (3) multi port, downstream, before valve, dedicated to each cylinder (4) direct injection, into cylinder
stratification?
Richer mixture near spark plug (needed for ignition) and leaner otherwise
allowing average leaner mixtures to burn with corresponding lower combustion
temperatures
advantages of stratification?
i. Less heat loss
ii. Less knock problems
iii. Less emissions
knock?
uneven burning of fuel
carburetor choke?
choke – butterfly valve that restricts airflow before venturi and idle valve for
cold starts. Large pressure drop draws a lot of fuel (AF near 1:1) from capillary tube and idle
valve
idle valve?
provides fuel when throttle is closed
aftercooler?
Cools compressed air before SI engine intake, Avoids knock without lowering compression ratio
turbo lag?
Delayed turbocharger response after sudden throttle change while waiting for exhaust flow to
change, Time / engine cycles needed to accelerate turbine when throttle opens
What is generally the largest restriction to getting air into engines, especially at high speeds?
intake valves
what is vvc?
Varying times valve open, open duration, and overlap period
With variable valve control (VVC), how should the control of intake and exhaust valves change as the engine speed increases?
Better for intake and exhaust valves to open sooner, stay open longer, and have higher lift at
higher speeds
valve lift (imax)
distance the valve opens
where does stratification occur?
gasoline direct injection
supercharger disadv and adv
Cons – parasitic engine load, cost, weight and noise
Pro – quick response throttle changes
supercharger?
Intake system compressor, mechanically driven of the engine crankshaft, that raises the
pressure of incoming air
turbocharger?
intake system compressor, powered by a turbine mounted in exhaust flow, that raises
the pressure of incoming air
