Fuel Injection Rate Control; Outline - Denso 4D56 Service Manual

12. FUEL INJECTION RATE CONTROL

12.1 Outline

While the injection rate increases with the adoption of high-pressure fuel injection, the ignition lag, which is the delay from the time
fuel is injected to the beginning of combustion, cannot be shortened to less than a certain value. As a result, the quantity of fuel that
is injected until main ignition occurs increases, resulting in an explosive combustion at the time of main ignition. This increases both
NOx and noise. For this reason, pilot injection is provided to minimize the initial ignition rate, prevent the explosive first-stage com-
bustion, and reduce noise and NOx.
Injection Rate
Heat Release
Rate
-20
Crankshaft Angle (deg)
Normal Injection
Large First-stage
Combustion
(NOx and Noise)
TDC 20 40
Operation Section
Pilot Injection
-20
TDC 20
Crankshaft Angle (deg)
1 35
–
Small First-stage
Combustion
40
QD2362E