*3.1. Average Mass Flow Rate*

The equations for calculating the experimental mass flow rate to obtain the discharge coefficient is as follows. The average mass flow rate of the intake air .*mexp* was measured with a laminar flowmeter using Equation (1) [22].

$$
\dot{m}\_{\rm exp} = Q\_{\rm l} \times \rho\_{\rm hv} \tag{1}
$$

where *Qt* is the volumetric flow rate and calculated using Equation (2).

$$Q\_t = K\_{20} \times \left(\frac{\mu\_{t(20^\circ \text{C})}}{\mu\_{t(intakx)}}\right) \times P\_{\text{x} \prime} \tag{2}$$

where *K*20 is the laminar coefficient under standard conditions, μ*t* is the viscosity depending on the air temperature, and *Px* is the differential pressure of the laminar flowmeter measured using a differential pressure meter. The average value measured during 100 revolutions for each engine speed was used, and the values are shown in Table 2.

**Table 2.** Differential pressure according to the engine speed.


ρ*h* is the density of moist air and was calculated using Equation (3).

$$
\rho\_h = \rho\_d \times \frac{1+\mathbf{x}}{1+1.609\times\mathbf{x}'},\tag{3}
$$

where ρ*d* is the density of dry air, *x* is the absolute humidity, and the values of each coefficient are shown in the Table 3.



*J. Mar. Sci. Eng.* **2020**, *8*, 1036
