*2.3. Installation Modifications*

The test engine was modified to run diesel/LPG dual fuel. A second injector housing was placed on the diesel engine cylinder head and the Magneti Marelli brand GDI injector was installed. LPG and diesel injector locations are shown in Figure 1. In order to control GDI injector, the angular piston position data which was obtained from an encoder coupled to the crankshaft was used. The ECU controlled the LPG injection timing and duration by evaluating the angular position data. To measure the instantaneous mass consumption of diesel and LPG fuels, electronic scales with precise measuring capability were used. A nitrogen cylinder with 200 bar operating pressure and pressure regulator were used to adjust LPG injection pressure. The liquid phase LPG that accumulates at the bottom of the LPG tank is transmitted to the GDI injector through a high-pressure fuel line. Thus, LPG injection in the liquid phase is provided via GDI injector.

**Figure 1.** LPG and diesel injector locations.

An Opkon brand PRI 50 model incremental optic rotary encoder coupled to the crankshaft was used for determining the angular piston position. As shown in Figure 2, the encoder has three output channels, A, B, and Z. Channel B leads Channel A by 90 degrees phase shift. Channel Z produces a pulse in every full turn of the encoder. A and B channels are used for rotation direction and position information while Z channels are used for rpm measurement. Direction sensing is determined by generating separate pulse trains for CW and CCW direction. A pulse train is generated by checking for falling edges on A or B pulses when other pulses are high. For position measurement, one pulse train adds to a count register and the other subtracts from a count register. Thus, a precise position detection was ensured, and the LPG injector was controlled with an appropriate timing. The GDI injector was triggered either by the injection of LPG into the cylinder or just after that ignition of the diesel fuel injected into the cylinder.

**Figure 2.** Encoder output signals.
