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Metafuel 2 system description

ECE R110 and ECE R115 compliant, EOBD compatible

MASTER-SLAVE system for bi-fuel vehicles

METAFUEL 2

METAFUEL 2 system description

Metafuel 2 system description.doc di 10

Summary Summary..............................................................................................................................2

General description ..............................................................................................................3

METAFUEL 2 features..............................................................................................................5

Injection pulse duration conversion................................................................................5

Air/Fuel ratio correction in WOT.......................................................................................5

Air/Fuel ratio correction in Warmup................................................................................5

Air/Fuel ratio correction in transient conditions ............................................................5

Spark Advance optimisation for CNG............................................................................6

Fuel quality recognition.....................................................................................................6

Other strategies ..................................................................................................................7

General electrical scheme ..................................................................................................8



General description A ECE R110 and ECE R115 compliant, EOBD compatible

MASTER-SLAVE system for bi-fuel vehicles

The Metafuel 2 system is a Multipoint Sequential Electronic Injection system based on the Master – Slave concept designed to convert original Otto cycle (Spark Ignition) engine from only gasoline to Bifuel CNG-Gasoline.

The Master-Slave concept is based on the application of control strategies operating in the gasoline Engine Control Unit (ECU), defined as Master, to the alternative fuel, after a dedicated adaptation of the injection parameters. The adaptation is done by the CNG ECU, defined as Slave, and it is necessary in order to keep into account the different physical and chemical characteristics of the fuels. The Slave ECU, therefore, is not provided with the typical “fuel metering” strategies based on speed density or MAF sensor, but uses the gasoline ECU ones.

Figure 1 - The Master-Slave concept scheme

The most evident advantage, from the application point of view, is the time saving for calibration: in an ideal situation only injector model adaptation parameters should be calibrated. In real world, taking into account that the same engine operates in different ways while fuelled with the different fuels and that the air/fuel ratio for gasoline outside the closed loop area (stoichiometric) is wrong for CNG, several CNG dedicated strategies must be applied in order to get the best performances and emission features required by actual vehicle applications.



From the point of view of the system, another big advantage of the Master-Slave system is the possibility to convert a complex gasoline engine with electronic injection to bifuel without modify the original gasoline ECU neither for SW or HW. Just few adaptations of the wiring harness are necessary and they don’t take too much development work and money.

Along with the base simplified concept of the Master-Slave control, the OEM quality that cannot be renounced, is ensured by the full compliancy of the system components to ECE R110 Standard and by the long lasting application of them to hundreds of thousands of passenger cars, light duty and heavy duty vehicles.

Finally, for those market where it is required, the ECE R115 Standard specifies that the CNG engine control could be fitted without a dedicated EOBD system, but while running on CNG, the vehicle emission compliancy must be ensured by the gasoline ECU control: in other words the EOBD system on the gasoline ECU must be fully operating and kept in complete efficiency also when the vehicle operates with a different fuel managed by a different ECU. The Metafuel 2 system has been tested by means of endurance tests for thousands of kilometres.



METAFUEL 2 features Injection pulse duration conversion This is the base strategy of the Master-Slave injection system concept.

The conversion factor between the duration of gasoline injector pulse and the CNG one is calculated by means of the measure of pulsewidth of the gasoline injector commands, whose electrical lines are connected to the CNG ECU. The pulse duration is proportional to the quantity of gasoline delivered and by means of the Air/Fuel ratio, the air mass flow is known. Starting from the intaken air mass flow it is possible to calculate the CNG quantity that must be delivered to the engine and through the CNG injector model, the duration of the CNG injector pulse is defined. The transfer strategy operates in real time (gasoline pulse measure, transfer calculation, CNG injector pulse operation) allowing the system to apply cylinder by cylinder what defined by the gasoline system.

From the HW point of view must be remarked that injectors emulator for gasoline ECU diagnosis is included in the Metafuel 2 ECU.

Air/Fuel ratio correction in WOT In Wide Open Throttle conditions the best performances as well as catalyst temperature control are usually obtained on gasoline fuelled engines by means of heavy enrichment of the air fuel mixture (usually 10%, in some cases much more for catalyst temperature reasons). These Air/Fuel ratios are not useful or even dangerous for CNG fuelling. A dedicated strategy for WOT condition detection, based on redundant signal comparison, and a tuning cartography are available to remove the unwanted enrichment derived from gasoline tuning. This resolves in better performance, driveability and fuel saving.

Air/Fuel ratio correction in Warmup Wall wetting formation occurring heavily while engine is in cold condition is compensated in gasoline mode with a general enrichment. Gaseous fuels like CNG are not affected by this behaviour. In order to get better performances and driveability in warmup while running on CNG the gasoline base enrichment must be avoided. A water temperature based strategy allows the tuning of fuel amount reductions.

Air/Fuel ratio correction in transient conditions Wall wetting formation affects the transient behaviour of gasoline fuelled port fuel engine. Since CNG is not affected by the wall wetting phenomena, if the



enrichment of gasoline operated while in transient condition is applied to CNG injection, poor driveability can occur. Therefore while a load transient is detected, a fuel reduction must be done by means of dedicated strategy.

Spark Advance optimisation for CNG Best performance, driveability and emissions are mainly affected by the spark advance applied. A general fixed shift of few degrees, usually operated with a Gasoline to CNG conversion in a gasoline base tuned engine, can help to get best performance tuning (usually max power) but it is not useful or even dangerous for driveability and emission features. Due to this reason the Metafuel 2 system has the possibility to tune a complete and high resolution cartography of spark advance optimisation (even spark retard could be applied).

Figure 2 - Spark Advance adder shifting device scheme

The spark advance added value can be continuously adapted while running on CNG taking into account engine operating mode (WOT or low load, low or high speed, idle). As already described for the injection, for the ignition management, the Slave ECU takes engine speed and camshaft signals from sensors, changes them with an angle – time – angle shift strategy, and replicates to gasoline ECU the wanted angular adaptation.

Fuel quality recognition Methane contents in commercial CNG can vary from filling station to filling station. The fuel self adaptation of the gasoline ECU (on which the Slave ECU thrusts) can be saturated when engine, injection system and fuel drifts are all in the same direction (i.e. sum of lean condition while -5% injectors, +5% engine intake efficiency, -2 % closed loop accuracy, -15% methane contents on CNG exceeds the usual ± 25 % authority). Basing on a fuel refilling detection strategy joined with a reference injection time with reference fuel tuning, a fuel quality recognition



strategy operates in CNG mode, leaving to gasoline self adaptation just its normal duty.

Other strategies An ECU has some low level strategies that are necessary to implement the high level functions (as the ones depicted above). The following table shows all the base functions included by the Metafuel 2 system Software.

1 Input signals SW, tied to the HW, dedicated to input signal conditioning and scaling

2 Output signals SW that takes care of the generation of pulse width, analog and digital signal applied to gasoline ECU, gasoline injectors, CNG injectors

3 Injection Timing Strategy dedicated to the CNG injection timing for optimisation of the fuel delivery and intake.

4 Cut Off Dedicated cut off strategy for better driveability as well as fuel saving features while running on CNG

5 Gas/Gasoline/Gas switchover

Strategy that manages all the fuel mode changes required or necessary (driver request or run out of Gas)

6 Power latch Post key-off strategy for EEPROM setting when engine is turned off

7 Diagnosis A complete set of diagnosis strategies that cover all external (input and output signals) and internal HW core components. It must be remarked that the diagnosis plug could be shared with gasoline ECU. CNG ECU can answer diagnosis devices with a dedicated address and the answer can be customised to the vehicle manufacturer standard.



General electrical scheme of the whole system Notwithstanding every application has its own gasoline components, more or less the most usual scheme that occurs while applying the Metafuel 1 system, is the one shown in the following picture.

Take care that:

• A complete and detailed electrical scheme is dependent on the original wiring harness and components of the application. The following scheme indicates the macro breaks, shunts and connections present in the Metafuel 1 system

• All power actuations are remotely operated by relais and protected by fuses that are too complex to be depicted for the scope of the following scheme

• Except for the Metatron supplied components, all other gasoline ones are only examples figures

• Only electrical wired components are included in the electrical scheme

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