**3. Results and discussion**

#### **3.1 Brake-specific fuel consumption (BSFC)**

**Figure 6** is the variation of brake-specific fuel consumption with full load under the effects of EGR percentage flow rate. Lower ratio blends of WPPOB10 and WPPOB20 show minimal reduction in the brake-specific fuel consumption (BSFC) at 0% EGR flow rate in **Figure 6** compared with the values of conventional diesel and WPPOB100, which are showing significantly high values of brake-specific fuel consumption (BSFC) at that mode. At 0% EGR, flow rate conventional diesel has a brake-specific fuel consumption value of 0.4 g/kW.hr., compared with WPPOB100 with a value of 0.4751 g/kW.hr. In other words, blend WPPOB100 has a higher brakespecific fuel consumption than diesel. The values for the other blends of WPPO are placed at 0.3225 g/kW.hr., 0.3615 g/kW.hr., 0.3645 g/kW.hr. and 0.3715 g/kW.hr., for WPPOB10, WPPOB20, WPPOB30 and WPPOB40 at this point, respectively.

**Figure 6.** *Brake-specific fuel consumption (BSFC) versus EGR percentage flow rate full load engine conditions.*

Similar trends are reported with application of EGR percentage flow rate such as at 20–25% EGR flow rate. At this point, the BSFC showed increasing tendencies, which is identical to the findings of [34]. This phenomenon is due to the effects of dilution of the fresh air intake as it mixes with exhaust gases. This mixture comes from the recirculated EGR system gases leading to incomplete combustion of the inducted mixture, hence a drop in power and engine torque. This scenario increases engine fuel consumption to maintain constant engine speed to meet increased load demand, which reflected increased BSFC. These findings are identical to the findings of [35].

The WPPO biodiesel blends showed better fuel economy with EGR percentage flow rate application. This is true especially for lower blend ratios of WPPOB10 and WPPOB20 compared with conventional diesel test fuels. However, increased EGR percentage flow rate increased the BSFC across all the test fuels used. For example, at 0% EGR, conventional diesel was 0.4 g/kW.hr. compared with 0.495 g/kW.hr. with application of 30% EGR flow rate. On the other hand, blend WPPOB10 was 0.3225 g/ kW.hr. compared with 0.5780 g/kW.hr. with application of 30% EGR flow rate.

**Figure 6** shows that the highest BSFC among the blends of diesel and conventional diesel test fuel is from blend WPPOB100. This blend at 0% EGR flow rate had a value of 0.4751 g/kW.hr. compared with 0.7235 g/kW.hr. at 30% EGR flow rate. During experimentation with 10% EGR flow rate, the values for the BSFC across all the test fuel seemed to pick a lineal increment trend as in **Figure 6**. This was indicated by the flattening of the graph curves with close-packed value trends.

#### **3.2 Brake thermal efficiency**

The aim of brake thermal efficiency is to help us to understand the ability of the combustion system to utilize the fuel provided. Furthermore, it is a means of comparing and assessing how efficiently fuel conversion was carried by turning it into mechanical output [27, 28]. **Figure 7** is brake thermal efficiency (BTE) % variations, under different blends of WPPO and conventional diesel fuel, with EGR % flow rate.

**Figure 8** is variation of the brake thermal efficiency with EGR % flow rate using different blends of WPPO and CD. In this figure, a decrease in the brake thermal efficiency with all high blend ratio fuel such as WPPOB40 and WPPOB100 is indicated compared with conventional diesel fuel. However, blend WPPOB100 has the lowest decrease of brake thermal efficiency at 7.05%, with 10% EGR flow rate. The value drops further to 2.35% with application of 30% EGR flow rate.

**Figure 7.** *Brake thermal efficiency (BTE) versus engine load percentage.*

*The Influence of Exhaust Gas Recirculation on Performance and Emission Characteristics… DOI: http://dx.doi.org/10.5772/intechopen.105011*

**Figure 8.** *Brake thermal efficiency (BTE) % versus EGR % flow rate.*

In other words, there is a reduction in the brake thermal efficiency due to the application of EGR percentage flow rate as shown in **Figure 8**. For example, at 0% EGR flow rate, brake thermal efficiency for conventional diesel is 12.15% compared with WPPOB10 and WPPOB20 at 13.25% and 13.05%. The WPPOB100 blend has the lowest value for thermal efficiency for all EGR rate flow modes than any other test fuel as shown in **Figure 8**.

#### **3.3 Brake power (BP)**

**Figure 9** shows brake power variations with different blends of WPPO and conventional diesel fuel at full engine load. The results obtained show that there is a lineal increase in the brake power for all the test fuels applied with increase in engine load. Conventional diesel fuel has the highest increase in brake power values compared with the blends of WPPO. At 20% engine load, conventional diesel is at 1.45 kW while WPPOB10 has a value of 1.350 kW representing a difference of 6.8% in BTE when the two fuels are compared.

**Figure 9** also shows very close unitary increments with increase in engine load conditions. It also shows a decrease in brake power as the blend ratio increased for all

**Figure 9.** *Engine brake power versus varying engine load percentage.*

the fuels tested. In other words, the increase in blend ratio showed a direct decrease in brake power linearly. For example, at 30% engine load CD, WPPOB10, WPPOB20, WPPOB30 and WPPOB40 reported values of 2.125 kW, 2.15 kW, 2.05 kW,1.98 kW, 1.86 kW and 1.75 kW, respectively, thus, showing a decrease in the value of the engine brake power throughout the experimentation and analysis period. Blend WPPOB100 showed the lowest values for the engine brake power compared with the blends of WPPOB10, WPPOB20, WPPOB30 and WPPOB40. These findings are identical with the findings of a research on WPPO blends [20].

The application of EGR percentage flow rate does not show significant changes in brake power. However, there is a negligible drop in the engine brake power application of EGR flow rate except for the blend WPPOB10. The blend has almost identical values to conventional diesel as the curve of the two fuels indicates in **Figure 9**; therefore, leading to a conclusion that the blends of WPPO have identical brake power values with conventional diesel.

#### **3.4 Exhaust gas temperature (EGT)**

Temperature is one of the key factors in determining the formation of engine exhaust emissions, besides providing or helping in the analysis and study of combustion processes in relation to fuel [36]. The result in **Figure 10** is showing a variation in exhaust gas temperature (EGT) with different fuel blends of WPPO and conventional diesel with the application of EGR percentage flow rate. The result indicates that EGT decreases with different blends of WPPO compared with conventional diesel test fuel.

The difference between conventional diesel and WPPO blends is the temperature increases in all the test conditions reported. However, it should be mentioned that as the blend ratio increased with EGR % flow rate application, the exhaust gas temperatures reduced significantly especially for WPPOB30 and WPPOB40 at 0% EGR flow rate, the highest temperature value obtained for conventional diesel is 456°C compared with WPPOB100 blend at 490°C. needless to mention at 30% EGR flow rate this blend has most reduction in temperature compared with the other WPPO blends with a temperature value of 320°C.

Applying increasing rates of EGR % flow rate modes as in **Figure 10** reduces exhaust gas temperature. For example, at EGR percentage flow rate of 5%, the

**Figure 10.** *Exhaust gas temperature (EGT 0 C) versus EGR percentage flow rate.*

*The Influence of Exhaust Gas Recirculation on Performance and Emission Characteristics… DOI: http://dx.doi.org/10.5772/intechopen.105011*

highest value for conventional diesel test fuel obtained was 440°C. The minimum value was 340°C obtained at 30% EGR flow rate. This trend is repeatedly shown for other WPPO blends with the application of EGR percentage flow rate such as blend WPPOB10 with a high value of 467°C and the lowest being 362°C at 5% and 30%, respectively. On the other hand, WPPOB40 shows its highest value as 472°C and the lowest as 330°C when applying 5% and 30% EGR flow rate, respectively.

The reduction in exhaust gas temperature among the different blends of WPPO was due to low calorific value of the blends and the low exhaust loss. This result is identical to the findings of [37, 38]. According to results shown in **Table 2**, WPPO has a calorific value of 40.15 kJ/kg compared with the calorific value of conventional diesel at 44.84 kJ/kg. The third cause is the effects of dilution, chemical and thermal factors brought through exhaust gas recirculation rate flow [39, 40].

#### **3.5 Hydrocarbon emissions**

**Figure 11** is a variation of hydrocarbon emissions in parts per million under full engine load with the application EGR percentage flow rates, using different blends of WPPO and conventional diesel (CD). All the blends of WPPO tested indicated significantly higher hydrocarbon emissions, especially with higher engine load conditions as shown in **Figure 11**. However, conventional diesel still produced more and higher values of hydrocarbon emissions compared with all the blends of WPPO across all the engine loading conditions and operating modes.

For example, when the EGR percentage flow rate is 0%, in other words, no application effect, **Figure 11** shows there is less hydrocarbon emissions for all the test fuels. The following values were reported 22 ppm, 23 ppm, 21 ppm, 20 ppm, 19 ppm and 17 ppm for WPPOB10, WPPOB20, WPPOB30, WPPOB40 and WPPOB100 respectively compared with 20% EGR percentage flow rates with 77 ppm, 68 ppm, 52 ppm, 46 ppm, 44 ppm and 40 ppm, respectively.

The application of EGR percentage flow rate reduces the amount of hydrocarbon emissions emitted across board all test fuel blends. However, conventional diesel fuel produced more hydrocarbon emissions compared with all WPPO blends tested. For example, **Figure 10** shows that at EGR flow rates of 5%, 10%, 15%, 20%, 25% and 30%, conventional diesel had 43 ppm, 57 ppm, 70 ppm, 82 ppm and 85 ppm, respectively. On the other hand, the values for WPPOB10 were 23 ppm, 35 ppm, 40 ppm,

**Figure 11.** *Unburnt hydrocarbons emissions versus EGR percentage flow rate.*

48 ppm, 50 ppm and 52 ppm, respectively. Therefore, the application of EGR percentage flow rate increased hydrocarbon emissions values as presented in **Figure 10**.

## **3.6 NOX emissions**

The formation of NOX emission is dependent on cylinder temperature, the concentration of oxygen and the residence time spent in the combustion chamber by the fuel-air mixture during phase of pre-mixing [41]. All tested blends indicated a drop in NOX emissions with the application of EGR percentage flow rate, at all engine load conditions. This was due to the rise in the total heat capacity of the working gases as EGR % flow rate increased, which was identical with the studies and findings of [42–44]. **Figure 12** shows NOX emissions value for the conventional diesel was 920 ppm at full load without EGR percentage flow rate, compared with WPPOB100 at 1270 ppm. However, with application of EGR percentage flow rate of 30%, the values reduced to 401 ppm for CD and 432 ppm for WPPO100, respectively.

However, during study, engine part load values in **Figure 13** for NOX emissions reported lower values compared with the full load engine conditions for the same test fuels. The NOX emission for conventional diesel at 50% (engine part load) was 635 ppm compared with full load at 1100 ppm. On the other hand, the value for WPPOB100 at 50% (engine part load) was 850 ppm compared with 1250 ppm at full engine load. This result concurs that at 50% (engine part load), the values of NOX emissions emitted by tested blends of WPPO except WPPO100 were lower compared with full engine load conditions.

#### **3.7 Carbon monoxide emission**

**Figure 14** shows variations of carbon monoxide emission percentage with varying load under the effects of EGR percentage flow rate, with different fuel blends of WPPO and conventional diesel fuel. As a gas, carbon monoxide is toxic and requires control to acceptable levels. Carbon monoxide is a product of poor combustion of hydrocarbon fuels due to dependency on the air-fuel ratio relative to the stoichiometric proportions [42].

In the experiment conducted, the amount of carbon monoxide emissions decreased with engine loads up to part load (50%). For example, at 0% engine load,

**Figure 12.** *EGR percentage flow rate variations with NOX emissions.*

*The Influence of Exhaust Gas Recirculation on Performance and Emission Characteristics… DOI: http://dx.doi.org/10.5772/intechopen.105011*

#### **Figure 13.**

*Variations of NOX emissions (ppm) versus varying engine load percentage without application of EGR flow rate.*

**Figure 14.** *Carbon monoxide emissions percentage versus varying engine load.*

the value of conventional diesel is 0.051% compared with 50% engine load when the value dropped to 0.03% by volume. However, the CO emissions continued to increase significantly but marginally as in **Figure 14** as the load increased from this point. Increasing the engine load from 50% recorded continuous but marginal increases of carbon emissions by volume across all the test fuels irrespective of the EGR percentage flow rate. For example, at 80% engine load, the value for WPPOB100 is 0.02% up from 0.0165% by volume. The other WPPO biodiesel blends also show a similar trend and concurrency. WPPOB20 and WPPO30 test fuels at 50% engine load condition have values of 2.25% and 2.15% as compared with 3.36% and 2.95% respectively, at 80% engine load.

**Figure 15** is the variation of carbon monoxide with EGR percentage flow rate application under conventional diesel and different blends of WPPO. The WPPO blends produced continuous increase in smoke emissions almost doubling values with the application of EGR percentage flow rate. For example, at 10% EGR flow rate, the carbon monoxide emission values were 9.79%, 10.46%, 10.91%, 11.25% and 12.75% for WPPO10, WPPO20, WPPO30, WPPO40 and WPPO100, respectively.

**Figure 15.** *Carbon monoxide VS EGR percentage flow rate application.*

The application of same EGR percentage flow rate reports the lowest carbon emissions with a value of 7.65% for conventional diesel test fuel.

The blend ratio and EGR percentage flow rate have a correlation on the amount of CO emissions produced. In other words, increased blend ratio increased carbon monoxide emissions within the blends as the EGR percentage flow rate increased. For example, at 20% EGR flow rate, CO emission values recorded were 18.25%, 21.35%, 22.65%, 24.55%, 26.95% and 28.85%, respectively. These values are for CD, WPPO10, WPPO20, WPPO30, WPPO40 and WPPO100. However, blend WPPO30 reports values of 4.85%, 7.28%, 10.91%, 16.37%, 24.55%, 35.75% and 52.69% as the EGR flow rate increased to 30%, respectively. This is caused by dilution, thermal and chemical effects of EGR % flow rate application as some of the oxygen in the inlet charge is replaced with recirculated exhaust gas that causes incomplete combustion.

### **3.8 Carbon dioxide emissions**

Carbon dioxide is the principal composition of the exhaust gas recirculation gases. However, carbon dioxide gas and the exhaust temperatures are indicators of combustion quality in the combustion chamber [6]. Carbon dioxide gas has a higher heat capacity making it a thermal heat sink during the combustion process. This helps in reducing peak cylinder temperatures, hence the reduction in the NOX emissions.

The value of CO2 is considerably high without EGR percentage flow rate coupled with lower engine loads for all the fuel blends tested. For example, at 20% engine load blend WPPOB100 has 4.65% compared with all the other test fuels and is the highest carbon emissions value. The other blends reported are CD, WPPO10, WPPO20, WPPO30 and WPPO40 with 3%, 2.50%, 1.5% and 1.85% respectively, as shown in **Figure 16**.

Additionally, **Figure 16** shows that the amount of carbon dioxide increased with increased engine load. For example, as the engine load increases to 40%, the value of WPPOB40 is 2.75% compared with WPPOB30 at 3.25% while at 70% engine load, the values are 4.5% and 5.25%, respectively. The observation is that as the engine load is increased with increased blend ratios, lower-ratio blends are observed to emit more carbon dioxide emissions as compared with those blends with high ratios except blend WPPOB100 that releases more carbon emissions than any test fuel as aforementioned earlier. At full engine load, the value of carbon dioxide emissions is at the highest

*The Influence of Exhaust Gas Recirculation on Performance and Emission Characteristics… DOI: http://dx.doi.org/10.5772/intechopen.105011*

#### **Figure 16.**

*Variation of carbon dioxide percentage emissions versus engine load percentage, with different types of fuel blends of WPPO and conventional diesel.*

#### **Figure 17.**

*Variations of carbon dioxide percentage versus EGR percentage flow rate, with different types of WPPO fuel blends and conventional diesel.*

values as in **Figure 16** across all the test fuels. The values are 12.75%, 10.85%, 9.65%, 8.75%, 8.35% and 8% for WPPOB100, CD, WPPOB10, WPPOB20, WPPOB30 and WPPOB40, respectively.

The application of EGR percentage flow rate increases the carbon dioxide emissions exponentially by almost doubling the values as can be seen in **Figure 17**. For example, at 10% EGR flow rate, the value of conventional diesel is 5.35% compared with WPPOB100 at 7.25%, WPPOB10 at 4.75%, WPPOB20 at 4.25%, WPPOB30 at 3.95% and WPPOB40 at 3.65%, respectively. This result reinforces the idea that there exists a correlation between blending and the EGR percentage flow rate with carbon dioxide emissions. Hence, the conclusion that the higher the blend ratio, the higher the emissions values and vice versa with application of EGR percentage flow rate. For example, at 30% EGR flow rate, all test fuels show high carbon dioxide emission, such as conventional diesel at 10.95%, WPPOB10 at 9.95%, WPPOB20 at 9.65%, WPPOB30 at 8.85% and WPPOB100 at 14.35%, respectively.

#### **Figure 18.**

*Variation of smoke emissions or opacity % versus EGR % flow rate, with different WPPO blends and conventional diesel.*

#### **3.9 Opacity emissions**

Smoke opacity emissions are defined as the solid hydrocarbon soot particles found in the exhaust system exit gases and linked to the formation of smoke emissions [45]. All tested blends of WPPO showed increased and aggravated levels of smoke emissions. However, they were of lower values compared to conventional diesel values.

**Figure 18** smoke emissions under the influence of EGR % flow rate using different WPPO blend and conventional diesel.

The incessant increase in smoke emissions in this figure is explained by high kinematic viscosity and the low volatility values of WPPO blends compared with conventional diesel test fuel. Furthermore, the poor injection and spray characteristics of WPPO blends of fuels compared with the spray and injection characteristics of conventional diesel fuel cause this phenomenon. WPPO blends are also associated with the high aromatic compounds compared with conventional diesel test fuel, hence the poor spray and injection quality.

The application of EGR percentage flow rate shows significant increases in the values of smoke emissions across all the test fuels. Blend WPPOB10 shows smoke emission of 7.2% lower compared with conventional diesel at 0% EGR flow rate. On the other hand, conventional diesel reports 11.5% higher emissions than WPPOB100 blend fuel when EGR flow rate is at 30%. This result is identical to the study findings of the following researchers [46].

The WPPOB10 blend emits the highest levels of smoke emissions for the blended fuels compared with the other WPPO fuel blends. In experimental analysis, blend WPPOB100 is the second highest emitter of smoke emissions. However, as the blend ratio and the EGR percentage flow rate increased, the smoke emissions increased incessantly across all the test fuels compared with EGR percentage flow rate of 0%.
