## 2 Materials and Methods  
### Experimental Set-Up and Measurement  
The research was carried out at the Center for Automotive Research and Electric Mobility, Universiti Teknologi PETRONAS. A single-cylinder, four-stroke, Yanmar diesel engine was modified to achieve the biogas delivery at the valve for in-cylinder mixing of the fuels. The technical information on the test equipment is presented in Table 1, while Figure 2 depicted the layout of the engine test rig. However, this research investigated the effects of direct-injected B5 and port-injected biogas delivered at the valve on the combustion, performance, and emission parameters. The concept aimed at eliminating air-fuel mixing before entering the cylinder, though delivered through the air intake manifold, thereby reducing the amount of mixture entering the crevices. To raise the in-cylinder temperature, thus reducing the pre-mature combustion at low load (4-7 bar IMEP). An injector holder and a delivery hose were developed and coupled to the air intake manifold to enable achievement of the gaseous fuel delivery at the valve for the in-situ mixing of the biogas and B5 in the cylinder. The delivery hose is a metallic tube of 4 mm inner diameter, connected at the end of the injector with the aid of the injector holder, through which the biogas was injected and delivered very close to the air inlet valve attaining nearly zero mixing rate and eliminated or minimizing the air-fuel mixing before entering the cylinder; hence, directly offered to the combustion chamber. The delivery hose was equipped with a gasket at its tip to minimize vibration, avoid direct metallic contact due to valve movement and enable biogas fuel flow control using intake valve closure. It was assumed that; the air and biogas maintained a forward flow direction, hence no gaseous fuel backflow to get mixed with the air before delivery into the cylinder otherwise, the quantity of biogas fuel that might backflow and gets mixed with the air, was assumed negligible.  
The eddy current dynamometer (DW10, 10 kw, 50 Nm, 13,000 rpm) was used for the measurement of engine load and speed while a rotary type encoder (E50S8-360-3-T-24) was utilized for the crank angle measurement. The engine used a pressure transducer to detect the pressure inside the cylinder. A hot-wire airflow meter was used to measure the airflow rate, range: 0-30 m/s, and a pressure sensor, range: \(-\)1 to 1 bar, was also used for the air pressure measurement. A K-type thermocouple, 0 to 1100 \({}^{\circ}\)C range, was employed to measure the air temperature. The information on the diesel mass flow rate and volume were obtained from the data acquisition system through a weighing scale attached to the engine control unit. However, a Linde HiQ pressure regulator was incorporated to decompress the biogas pressure to 2 bar, and its mass flow rate was measured using I  
\begin{table}
\begin{tabular}{c c} \hline
**Description** & **Specifications** \\ \hline Model & L100V \\ Type & Single cylinder, 4-stroke, air-cooled engine \\ Bore & 86 mm \\ Stroke & 75 mm \\ Displacement & 435 cm\({}^{3}\) \\ Compression ratio & 20.0 \(\pm\) 0.3 \\ Fuel injection timing & 21\({}^{\circ}\) CA BTDC \\ Continuous Rate Output & Engine speed & 3600 rpm \\ Output & 6.2 kW \\ Maximum Rated Output & Engine speed & 3600 rpm \\ Output & 6.8 kW \\ \hline \end{tabular}
\end{table}
Table 1: The technical specification of the test equipment (engine).  
Figure 2: An illustration of the engine test rig.  
An SPTC AutoChek gas analyzer (M-GS-V1.5 E IC) was also used to measure the NOx, UHC, CO, and CO\({}_{2}\) emissions with an accuracy of 1 ppm, 1 ppm 0.01%, and 0.01% respectively.