Ethanol & Flex Fuel Tuning: Introduction
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Introduction
02.56
| 00:00 | - Injection time based ECUs operate a little differently to the VE based ECUs we've just discussed. |
| 00:06 | Instead of modelling the air flow into the engine, injection time based ECUs directly request a specific injector pulse width from the main fuel table. |
| 00:16 | The numbers in the fuel table may be an actual injector pulse width or alternatively the ECU may use a fuel table where the values we enter are a percentage of a base injector pulse width. |
| 00:28 | Regardless of the way the fuel table is represented, the tuning process is very similar though. |
| 00:34 | In this type of ECU the fuel characteristics are typically ignored and we'll usually have no air fuel ratio target table, so we actually need to make adjustments to the numbers in the fuel table in order to achieve a richer or a leaner air fuel ratio. |
| 00:51 | Since the fuel characteristics and the stoichiometric air fuel ratio of the fuel are ignored, we need a slightly different approach to controlling the fuel delivery for a flex fuel system Typically the way the fuel delivery is dealt with for flex fuel in this type of ECU is via a second fuel table or alternatively a trim table which is used to vary the fuel volume delivery required to achieve or target air fuel ratios on our second fuel. |
| 01:18 | In this case we can apply what we've already learned through the course to decide on the required volume changes to suit our ethanol blend. |
| 01:27 | We've already seen that an E85 blend is going to require approximately 40% more fuel volume compared to gasoline for example. |
| 01:36 | If the ECU uses two separate fuel tables, then we can simply copy the numbers from our gasoline table into our ethanol table and then apply the required percentage compensation. |
| 01:48 | If on the other hand the ECU uses a fuel trim table, then we would apply the required trim percentage directly into this table. |
| 01:57 | While theory would suggest that we should be able to apply a constant percentage change everywhere in the table, this probably won't quite work out in reality, and we will need to still manipulate the trims for our second fuel during the tuning process dependent on the current load and RPM. |
| 02:15 | When it comes to cold start compensations, ignition timing, and boost control, injection time based ECUs operate in a similar fashion to a VE based ECU by providing a second set of tables and blend tables to define how the ECU interpolates between them. |
| 02:32 | An alternative here with the cold start correction and boost control is to use ethanol content as an axis instead of providing a completely separate table and a blend. |
| 02:44 | Now that we understand how this type of ECU deals with the changing ethanol content, we can move on and in the next module, we'll discuss the tuning technique. |
