3.2.3. The Effect of WPO Blends on Thermal Efficiency

Thermal efficiency is the ratio of work output to energy supplied through fuel injection. The variation of thermal efficiencies using WPO–gasoline blends and pure gasoline is shown in Figure 7. It can be seen that the brake thermal efficiency (BTE) for WPO-RON88-10, WPO-RON88-20, and WPO-RON88-30 were 16.09%, 17.08%, and 17.3%, whereas for RON88, the BTE was about 16.02% at engine speed 1500 rpm. Based on the results of the experiments conducted, the higher the engine speed, the lower the BTE, which can be attributed to increased BSFC at higher engine speeds. It can be seen that the thermal efficiency of content of WPO in WPO–gasoline mixtures was higher than that of pure gasoline, which can be attributed to less frictional power loss than that of lower WPO blends and pure gasoline. Similar results were obtained by Cleetus et al. [22], showing a higher percentage of WPO in WPO–gasoline blends resulting in higher thermal efficiency compared to that of lower WPO containing blends in a CI engine. In addition, higher oxygen content in high WPO blends can result in the presence of more oxygen in the combustion process, therefore achieving better combustion and hence greater thermal efficiency [39].

**Figure 7.** Effect of WPO-RON88 blend on thermal efficiency (%), compared to RON88.

#### *3.3. Engine Performance Fueled by WPO–Gasoline (RON 90) Blends*

Research has been conducted to examine the effect of engine power, SFC, and thermal efficiency on gasoline engines with high-speed motor using WPO–gasoline (RON 90) blends with different mixture variations.

#### 3.3.1. The Effect of WPO–Gasoline RON 90 Blends on Engine Power

From Figure 8, it can be seen that engine power increased with increase in engine speed. The rate of increase in power above 3000 rpm was slower compared to other engine speeds, which can be attributed to faster valve operation, reducing the mean effective pressure of the piston in the engine. It is shown in Figure 8 that the power generated from pure RON 90 fuel at 1500 rpm is 1.626 HP, while the WPO-RON90-10, WPO-RON90-20, and WPO-RON90-30 produced powers of 1.573 HP, 1.410 HP, and 1.205 HP, respectively. On the other hand, the engine speeds at 2000 rpm, 2500 rpm, and 3000 rpm for RON 90 produced powers of 2.260 HP, 2.697 HP, and 3.049 HP, respectively. The powers produced by WPO-RON90-10 is close to that of RON 90, which were 2105 HP, 2587 HP, and 2841 HP at 2000 rpm, 2500 rpm, and 3000 rpm, respectively. Furthermore, at 3500 rpm RON90 produced the highest engine power of 3.169 HP. Moreover, the WPO-RON90-30 produced close to the highest powers of pure RON 90, which were 3.078 HP at an engine speed of 3500 rpm, followed by WPO-RON90-10 and WPO-RON90-20, respectively. Ravinanath et al. [39] also reported similar results for higher concentrations (%) of WPO in the blend. As such, blends with higher concentration of WPO was able to approach the engine power output produced by RON90. The WPO-RON90-30 fuel blend produced the highest engine power compared to other blends due to the presence of more fuel-borne oxygen for combustion, therefore producing better combustion.

**Figure 8.** Effect of WPO-RON90 blends on engine power compared to RON90.

#### 3.3.2. The Effect of WPO–Gasoline RON 90 Blends on SFC

The SFC for WPO–gasoline blends as well as pure RON 90 fuels are shown in Figure 9. The SFC increased with an increase in the percentage of WPO in WPO–gasoline blends at the same engine speed. It can be seen in Figure 9 that at an engine speed of 2000 rpm, the SFC of WPO-RON90-10, WPO-RON90-20, WPO-RON90-30, and RON90 were 0.2304 kg/kWh, 0.2665 kg/kWh, 0.2976 kg/kWh, and 0.1388 kg/kWh, respectively. With the increase in engine speed from 2000 rpm to 3500 rpm, an increase in SFC was observed due to higher frictional loss at higher engine speed, as discussed previously. In a previous work, Murni [41] reported that the use of fuels with low kinematic viscosity can increase the amount of fuel being consumed during engine operation. Interestingly, at engine speeds between 1500 rpm to 2000 rpm, the SFC of every fuel is decreased, which is different from the results reported by Cleetus et al. [23]. This can be attributed to the high calorific value and octane number of RON90 fuel.

**Figure 9.** The effect of WPO-RON90 blend on SFC compared to RON90.
