MULTIPLE FUEL INJECTION CONTROL [SKYACTIV-D 1.8]

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Outline

•  Multiple fuel injection control has been adopted in which the number of fuel injections is divided over several times for the purpose of noise and NOx reduction.
―  For single injection, a greater amount of fuel is consumed to inject the necessary amount of fuel at one time. For this reason, the fuel is combusted rapidly at a high temperature and high pressure, resulting in increased noise and NOx.
―  In multiple injection, combustion is performed more slowly to divide the necessary fuel amount over several times, thus controlling noise and the occurrence of NOx.
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•  The PCM injects fuel several times prior to the main injection according to the vehicle operation conditions. (Pilot injection)
•  During diesel particulate filter generation control, fuel is injected after the main injection to increase the temperature. (Follow-up injection, post injection)
•  Fuel is injected after the main injection to switch to the rich combustion condition (λ<1) during DENOx/DESOx control. (Follow-up injection, post injection)

Block Diagram

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Operation

•  The PCM determines the number of fuel injections based on the fuel injection amount and signals from each sensor.
•  When the engine is started, the number of fuel injections is determined by the engine coolant temperature and the engine speed.
•  In the multiple fuel injection control, there are various patterns from the combination of the number of fuel injections.
•  The PCM selects the optimum pattern based on the vehicle conditions and performs fuel injection for a maximum of 8 times.
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Control range

Control description
Constant fuel injection
Low engine speed, low load
For the purpose of reducing engine knock occurring during combustion and to assure ignitability, the number of fuel injections is increased to a maximum of 6 times.
High engine speed, high load
Output and fuel consumption is improved by reducing the fuel injection time and injecting a higher amount of fuel over a fewer number of injections.
Rapid engine warm-up control
When the engine coolant temperature is low and the cabin heating performance is insufficient, 2 additional follow-up injections are performed to increase the exhaust temperature from the after-burn.
Diesel particulate filter regeneration control
During diesel particulate filter regeneration, fuel injection is performed at a slower timing than normal to remove particulate matter (PM) accumulated in the diesel particulate filter.
1.  Follow-up injection is performed after the main injection. (increases exhaust pipe temperature)
2.  Post injection is performed 1—5 times* (increases exhaust temperature necessary for combustion and removal of particulate matter (PM))
During DENOx/DESOx control
Fuel injection is performed at a slower timing than normal to break down the NOx stored in the NSC during DENOx control.
Fuel injection is performed at a slower timing than normal to break down the SOx accumulated in the NSC during DESOx control.
1.  Follow-up injection is performed to stably perform post combustion after the main injection.
2.  Rich combustion condition (λ<1) necessary for combusting the PM accumulated in the diesel particulate filter is produced by performing post injection one time.
Fuel-cut
During fuel-cut operation, fuel is not injected by the fuel injection amount control.
(See FUEL INJECTION AMOUNT CONTROL [SKYACTIV-D 1.8].)

*  :When the unburned fuel (HC) caused by the post injections reaches the oxidation catalytic converter, it is activated at the catalyst, and the exhaust gas temperature is increased. The division of the post injection into 1—5 times is for the purposes of reducing engine oil dilution and fuel adhesion to the cylinder walls. If fuel injection is performed at a slower timing than normal (timing in which no combustion occurs in cylinder), the fuel flows to the oil pan, and there is the possibility of the engine oil becoming diluted. In addition, by injecting small amounts of fuel in multiple stages, the penetration power of the atomized fuel is reduced and adhesion of fuel to the cylinder wall is prevented.

Regarding engine oil dilution from post injection

•  Although post injection, in which fuel injection occurs after the combustion process, is effective for DPF regeneration control by after-burn, fuel adhesion to the inside of the cylinder wall occurs with the possibility of engine oil dilution.
•  As for the symptoms of engine oil dilution, use the guidelines indicated in the table below. (The engine oil level changes dramatically depending on the oil temperature and the amount of time elapsed since the engine was turned off, thus there may be differences in the actual engine oil level.)

Item

Engine oil dilution
Engine oil dilution amount reference
Oil level gauge position
A
B
C
D
User action
If the wrench indicator light or oil warning light is not turned on, there is no problem.
Vehicle servicing at Authorized Mazda Dealer
Dealer action: Wrench indicator light turned on (P252F:00 stored)
Perform the diagnosis for an engine oil level sensor malfunction.
After verifying the engine oil level, replace the engine oil and implement the engine oil data reset using the Mazda Modular Diagnostic System (M-MDS).
Dealer action: Wrench indicator light turned on (No DTC)
After verifying the engine oil level, replace the engine oil and implement the engine oil data reset using the Mazda Modular Diagnostic System (M-MDS).
Dealer action: Oil warning light turned on (P253F:00 stored)
After verifying the engine oil level, replace the engine oil and implement the engine oil data reset using the Mazda Modular Diagnostic System (M-MDS).