Measuring Engine Performance

Part 2 – Measuring Engine Performance

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Figure 1. Brake Thermal Efficiency VS Engine Speed (Measured in lab).

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Figure 2.Brake Thermal Efficiency VS Engine Speed (From Internet).

Figure 1 and Figure 2 are both plot of brake thermal efficiency against engine speed. From figure 1, it can be seen that the thermal efficiency are generally decrease while engine speed increase from 2000 RPM to 4000 RPM, and the small shocks caused by experimental measure error. From the equation of brake thermal efficiency provide, the efficiency is related brake power, and the time of 5cc fuel used. The real brake thermal efficiency against engine speed shows in figure 2. The brake thermal efficiency increase from 1000 rpm to 3000 rpm to achieve 30% efficiency, after 3000 rpm, it has a small fall.

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Figure 3. Volumetric Efficiency VS Engine Speed (Measure in Lab)

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Figure 4. Volumetric Efficiency VS Engine Speed (From Internet).

Volumetric efficiency is measured the ratio of air that is trapped I the engine by the cylinder in static conditions, and it describes air intake process. In the case of forced induction, the volumetric efficiency can over 100 percent. From figure 3, the volumetric efficiency raise slightly from 2000 rpm to 3500 rpm, but after 3500 rpm, it decrease slightly as well, it basic follow the curve describe the real life case (Figure 4). The real volumetric efficiency will achieve 100% in 6000 rpm, and decrease slowly after that. However, the results of volumetric efficiency from lab is always exceeding 100%, and almost achieve 160%, which is doubtful.

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Figure 5. Torque VS Engine Speed

Figure 5 is a plot of torque against engine speed, generally speaking, the curve is increasing from 2000 rpm to 3000 rpm and achieve maximum torque 7.36 Nm, and after 3000 rpm, it is decreasing until 6.75 Nm in 4000 rpm. And this curve is almost follow the curve of torque and engine speed curve which searched on the internet.

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Figure 6. Brake Power VS Engine Speed (Measured in lab).

Figure 6 shows the plot of brake power against engine speed, the equation of brake power is related to brake power and speed, and the brake power increase as engine speed increase from 1400 W to 2800 W.