**2. Experimental Apparatus**

Figure 1 representing the experimental apparatus. The engine was a 35 kW three-cylinder direct injection four-stroke diesel engine. Intake and exhaust pipes were installed only in the No.1 cylinder to measure the intake and exhaust pipe pressure of a single cylinder. To observe the intake and exhaust gas flow in a cold flow state where no combustion reaction occurred, an electric motor was connected to a fly wheel in order to rotate. The mass flow rate was measured by installing a laminar flowmeter (LFE-100B, Tsukasa Sokken, Tokyo, Japan) at the starting point of the intake pipe, and the di fferential pressure of the laminar flowmeter was measured using a di fferential pressure transmitter (FCO332, Furness Controls, Bexhill-on-Sea, England) [19].

**Figure 1.** Photograph of the experimental apparatus.

Table 1 provides the specifications of the experimental apparatus. The intake air method was in a naturally aspirated state, and the experimental data were measured at intervals of 200 rpm in the range of 700–1500 rpm of engine speed. The intake pipe from the surge tank to the cylinder head was a straight pipe with a diameter of 0.04 m and a length of 0.5 m. The exhaust pipe was a straight pipe with a diameter of 0.04 m and a length of 1.0 m, and the end of the exhaust pipe was an open-end through which the exhaust gas was released into the atmosphere. CA◦ refers to the crank angle degrees.


**Table 1.** Specifications of the experimental apparatus.

Figure 2 shows a block diagram of the experimental system. The intake and exhaust pipe pressure was measured using a data acquisition (DAQ) system consisting of a piezoresistive amplifier and a rotary encoder (E6C2-CWZ3E, Omron, Kyoto, Japan) [20]. The pressure sensors were piezoresistive (4045A5, Kistler, Winterthur, Switzerland) and the measurement point was the intake and exhaust pipe 0.15 m away from the cylinder head. The data were acquired at intervals of 0.5 CA◦ during 100 revolutions while the engine was stable. In order to obtain an accurate measurement, the ensemble average was applied to measured data. The ensemble average was used as a method of calculating the average of remaining values excluding the top 10% and the bottom 10% of the measured data [21]. The pressure results of the intake and exhaust pipe obtained by the ensemble average were used to verify the results of the 1D gas flow analysis.

**Figure 2.** Block diagram of the experimental system. DAQ: data acquisition.
