For analyzing the gaseous emissions, a Horiba MEXA 7100 was used. The gaseous emissions include CO, THC, and nitrogen oxides (NOx), but aldehydes were not measured in this study. For the measurement of particulate mass and number, a Cambustion DMS 500 was used. The intake manifold pressure and the in-cylinder pressure were measured using a Kistler 4045A and a Kistler 6041A respectively. The pressure data acquisition was completed over 100 consecutive cycles with the VX-765 of 0.1 °CA, and the analysis of the combustion characteristics was conducted using an AVL Indi-Module. The Indi-Module software was incorporated to perform knock detection. The lambda value of the air–fuel mixture was measured using a Horiba λ analyzer.
2.2. Dual fuel injection system
The injection system used in bioluminescent study consisted of three injectors (see Fig. 2). A peak and hold type multi-hole GDI injector was used for delivering gasoline into the cylinder, and two saturation type PFI injectors were used for delivering ethanol to the intake port. The PFI injectors used in this study were designed to improve the atomization of the fuel and achieve a sauter mean diameter of approximately 50 μm under the injection pressure of 0.3 MPa. These injectors enabled the injection of ethanol while the intake valves were open, with a minimum penalty in the emission characteristics.