Staged Injection

Note: This function is visible only when the Injection Mode is set to Group/Staged or Sequential/Staged.

Staged injection uses primary injectors operating all the time and secondary injectors which operate only at higher load/rpm.  Both sets of injectors are controlled by the main fuel table (Fuel Table 1 or Fuel Table 2), however the percentage of the total fuel delivered by each injector set is controlled by the Secondary Injection Table.

The secondary injectors may be brought on at any stage by entering non-zero numbers into the Secondary Injection table.

Note:  It is very important that BOTH the primary and secondary injector duty cycles are closely watched to ensure that neither set of injectors are being operated at an excessive duty cycle.

The following functions control staged injection:

• Sec/Pri Ratio
• Secondary Injection Table
• Sec PW Lockout
• Accel Fuel
• Accel Time
• Load Axis
• Table Start
• Table Increment
• Secondary Injector Dead Time Table

Click on PCLink screen-shot to view "full screen"

Sec/Pri Ratio - Secondary to Primary Injector Flow Ratio

The Sec/Pri Ratio is ratio of the total secondary injector flow to that of the primary injectors.  This number must be entered before tuning.  If primary and secondary injector flow rate is unknown it will be necessary to determine these either from injector specifications or on an injector flow bench.  To calculate the correct number to enter as the Sec/Pri Ratio, divide the total secondary injector flow rate by the total primary injector flow rate.  Note that by total flow rate means the sum of all primary injector flows and sum of all secondary injector flows.
If the Sec/Pri Ratio is set too high then the engine will run leaner as the secondary injectors are activated.
If the Sec/Pri Ratio is set too low then the engine will run richer as the secondary injectors are activated.

Example:
If an engine has four 240 cc/min primary injectors and two 400 cc/min secondary injectors then the Sec/Pri Ratio is calculated as follows:

• ·    Total primary injector flow rate is 4 x 240 = 960 cc/min.

• ·    Total secondary injector flow rate is 2 x 650 = 1300 cc/min.

• ·    Sec/Pri Ratio is 1300 / 960 = 1.354.

Secondary Injection Table

The Secondary Injection Table is used to determine the percentage of the total fuel flow which is delivered via the secondary injectors.  This value can be changed depending on load.
The Load Axis of this table can be set to either MAP or MGP.  The start value of the load axis can be adjusted using the Table Start value.  The rate at which the load value increments can be set using the Table Increments value.

• A value of 0% represents complete fuel delivery through the primary injectors. The secondary injectors will be off.  Typically a value of 0% will be used at low load.
• A value of 50% results in half of the fuel being delivered by the secondary injectors.  
• A value of 100% represents complete fuel delivery through the secondary injectors. The secondary injectors will be off.

In typical applications the engine will run on the primary injectors at low load (0%).  Often as load increases the Secondary Injection Table values will increase until the secondary and primary injectors operate at the same pulse width.  Note that the Secondary Injection Table value required to give matched pulse widths depends on the size of the injectors in relation to each other.
The Secondary Injection Table value required to give equal pulse widths can be found by the following equation:

• Secondary Injection Table value for matched Pulse Width  = (100 * Sec/Pri Ratio) / (1 + Sec/Pri Ratio)

Example:

The following example calculates the required Secondary Injection Table value to give equal primary and secondary injector pulse widths.  Assuming the following information:

• Total Primary Injector Flow = 1100 cc/min.

• Total Secondary Injector Flow = 3200 cc/min.

• Sec/Pri Ratio = 2.9 (3200 / 1100 = 2.9

Therefore the Secondary Injection Table required for matched pulse widths:
Table Value = (100 * Sec/Pri Ratio) / (1 + Sec/Pri Ratio
                  = (100 * 2.9) / (1 + 2.9)
                  = 290 / 3.9
                  = 74.4 %

i.e. when the pulse widths are the same 25.6% of the fuel is delivered by the primary injectors, while 74.4% of the fuel is delivered by the secondary injectors.

Secondary Pulse Width Lockout

The Secondary Injection Table allows the secondary injectors to be activated either instantaneously or progressively.  If the Secondary injectors are activated progressively then there is potential for them to operate at very short pulse widths as they are introduced.  However, all injectors have a minimum pulse width for stable operation.  This can be up to a full millisecond more than the injector dead time. 

e.g. A particular injector may have a dead time of approximately 0.9ms, but it will not operate satisfactorily below 1.6ms.

The Sec PW Lockout is the minimum pulse width that the ECU will use for the secondary injectors.  If the ECU calculates a required secondary pulse width that is below this then the secondary injectors will stay off and all fuel will be delivered by the primary injectors (including the fuel that was calculated for the secondary injectors).  Once the ECU calculates a pulse width greater than the Sec PW Lockout value, fuel will be delivered through the primary and secondary injectors.
A typical value for Sec PW Lockout is between 1.0 and 2.0ms

Staging Acceleration Enrichment

In some applications the primary and secondary injectors are physically mounted in different locations.  Often the primary injectors will be mounted closer to the engine’s intake port with the secondary injectors further up the intake runner.  If there is a large distance between the two injectors then the engine will run lean momentarily as the secondary injectors are activated.  This occurs because the fuel delivered by the primary injectors has been reduced, but there is a delay in the secondary injector’s fuel reaching the engine.  To alleviate this problem the following functions have been added.

• Accel Fuel - This is the percentage enrichment used during the staging transition.
• Accel Time - This is the number of engine cycles that the staging enrichment will last for.      

Secondary Injector Dead Time Table

This table specifies the Secondary Injector Dead Time as a function of system voltage.

Copyright 2006 Link ElectroSystems