From the previous section, it can be concluded that
gasoline engines score well in terms of emissions (related
to local air quality), but have a relatively poor efficiency
(related to CO2 emissions, thus global warming), whereas
diesel engines are more efficient, but generally more
polluting. The more advanced engines currently in the
market, and new engine technology now being developed,
try to improve the weaker points while keeping the assets.
For instance, gasoline engine development is targeted
primarily at improving part-load efficiency, mostly through
minimizing throttle losses. Measures taken include variable
valve timing and lift, exhaust gas recirculation (EGR),
and Bdownsizing[ of the engine, using a smaller engine
while keeping the peak power. For a given load, the smaller
engine effectively needs to work harder, asking for larger
throttle openings resulting in a better efficiency. Keeping
the same peak power as the larger engine is enabled
through turbocharging (i.e., increasing the pressure of the
intake air, resulting in more mass per cycle, see above).
This will inevitably increase in-cylinder temperatures,
which increases the danger for auto-ignition (knock). This
can be counteracted by decreasing the compression ratio of
the engine, but as mentioned above this decreases the
engine efficiency. Modern engine technology allows the
From the previous section, it can be concluded that
gasoline engines score well in terms of emissions (related
to local air quality), but have a relatively poor efficiency
(related to CO2 emissions, thus global warming), whereas
diesel engines are more efficient, but generally more
polluting. The more advanced engines currently in the
market, and new engine technology now being developed,
try to improve the weaker points while keeping the assets.
For instance, gasoline engine development is targeted
primarily at improving part-load efficiency, mostly through
minimizing throttle losses. Measures taken include variable
valve timing and lift, exhaust gas recirculation (EGR),
and Bdownsizing[ of the engine, using a smaller engine
while keeping the peak power. For a given load, the smaller
engine effectively needs to work harder, asking for larger
throttle openings resulting in a better efficiency. Keeping
the same peak power as the larger engine is enabled
through turbocharging (i.e., increasing the pressure of the
intake air, resulting in more mass per cycle, see above).
This will inevitably increase in-cylinder temperatures,
which increases the danger for auto-ignition (knock). This
can be counteracted by decreasing the compression ratio of
the engine, but as mentioned above this decreases the
engine efficiency. Modern engine technology allows the
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