**4. Engine characteristics of WaFO and its dominant FAEs**

The evaluation of performance, emission and combustion characteristics of WaFO biodiesel was carried out in a Kirloskar TV1 single cylinder CI engine equipped with in-built water cooling system, with **Table 2** consolidates the product specifications of the test engine and flue gas analyzer used in this present study [15, 32]. Here, the parameters tested for this present study includes performance characteristics (specific fuel consumption and brake thermal efficiency), emission characteristics (mon- and di- oxides of carbon and nitrogen, unburnt Hydrocarbon emission, and exhaust gas temperature), and combustion characteristics (maximum in-cylinder pressure, ignition delay, heat release rate). For purpose of testing, two different types of samples


#### **Table 2.**

*Product specification of test engine and flue gas analyzer [15, 32].*

have been used in this study and are named as follows: blend samples and ester samples. In specific, blend samples consist of B10, B20 and B30 samples, with 10%, 20% and 30% of biodiesel blended in neat diesel, respectively; and will be used for assessing the trends of biodiesel's performance in engine. On the other hand, ester samples consist of characterized dominant FAEs, ethyl oleate, ethyl palmitate and ethyl stearate, blended in the concentration with respect to B20 blend; and are named as oleate blend, palmitate blend, stearate blend. For better understanding, the blending of blend and ester samples are represented in form of mathematical correlations Eqs. (2) and (3) [15]; and are used for calculating the volume of diesel and biodiesel/ ester required for making the necessary blends.

$$\text{Amount of diesel (ml)} = V\_{\text{overall}} \ast \left\{ \mathbf{1} - \left[ \mathbf{q}\_{\text{E}} \ast \mathbf{w}\_{\text{B}} \right] \right\} \tag{2}$$

$$\text{Amount of biodies} \,(\text{ml}) = \text{V}\_{\text{overall}} \ast \left\{ \text{q}\_{\text{E}} \ast \text{\textquotedblleft} \text{\textquotedblright} \right\} \tag{3}$$

Here, B20 blend was identified as ideal proportion for understanding the influence of FAEs in deciding the engine characteristics ofWaFO biodiesel; and was acknowledged due to the increased performance of any biodiesel at their 20% blend [34]. In addition, blending ester samples reduced the technical challenges associated with low temperature crystallization and increased viscosity, besides their cost. **Table 3** reports the overall engine characteristics of WaFO biodiesel blends, along with neat diesel averaged over their engine loads. For ensuring accuracy in results, all the experimental runs were performed in triplicates and are reported in form of mean � standard error, wherever applicable.

#### **4.1 Combustion characteristics**

#### *4.1.1 Maximum/peak In-cylinder pressure (Pmax)*

In general, in-cylinder pressure inside the cylinder signifies the degree of homogenous mixing of injected fuel with air, and helps in enhancing the rate of combustion. From **Table 3** and **Figure 1**, both blend and ester samples reported higher in-cylinder pressure against neat diesel sample owing to their higher cetane number, which shortened their ignition delay (ID), thereby allowing them to get combusted using


#### **Table 3.**

*Engine characteristics of blend samples, averaged over the engine load.*

*Molecular Contribution of Fatty Acid Esters in Biodiesel Fueled CI Engines DOI: http://dx.doi.org/10.5772/intechopen.102956*

**Figure 1.** *Maximum in-cylinder pressure of WaFO B20 blend and ester samples.*

their fuel bound oxygen content [32, 35, 36]. Accordingly, B10 blend reported 10.33%, B20 blend reported 12.64% and B30 blend reported 15.46%, higher peak in-cylinder pressure than compared to neat diesel. Likewise, stearate blend reported 3.27%, palmitate blend reported 5.1% and oleate blend reported 6.75%, higher peak in-cylinder pressure than compared to neat diesel.

Upon comparing ester samples with Biodiesel (B20) blend, oleate blend reported minimal variation in peak in-cylinder pressure by 5.52%, followed by palmitate blend and stearate blend reporting 6.72% and 8.3%, respectively. Here, the reduced peak pressure for palmitate and stearate blend signifies their early start of combustion (SOC) citing their shortened ID, besides their reduced concentration. In contrast, oleate blend reported marginal reduction in peak pressure, citing its unsaturation, which reduced its cetane number and prolonged its ID. This prolonged time delay accumulated a significant amount of fuel during premixed burn phase, and got combusted using the available fuel bound oxygen during the diffusion combustion phase [37]. Correlating this, presence of saturated FAEs (ethyl palmitate and ethyl stearate) in WaFO biodiesel initiated the early SOC during the premixed combustion phase, because of their higher cetane number; and provided sufficient activation energy for initiating the combustion of unsaturated FAEs (ethyl oleate, etc.) during the controlled combustion phase. Moreover, in-cylinder pressure increased with engine load for both blend and ester samples, considering the increasing amount of fuel combusted, intending to meet the energy demand of the engine.

#### *4.1.2 Instantaneous heat release rate (iHRR)*

More often, heat release rate curve briefs out about the time line of the combustion stroke, indicating the Start Of Injection (SOI), Ignition Delay (ID), Start of

Combustion (SOC); and ultimately, the amount of heat released during the combustion of fuel [38]. From **Table 3** and **Figure 2**, both blend and ester samples happened to report higher iHRR than neat diesel citing their early initiation of combustion and its prolonged duration, which provided adequate time for the accumulated low volatile fuel to undergo combustion during both premixed phase and diffusion combustion phase [39]. In addition, fuel bound oxygen played a crucial role in ensuring the complete oxidation of these FAEs in blend and ester samples. Comparatively, B10 blend reported 11.36%, B20 blend reported 12.97% and B30 blend reported 15.47%, higher heat release rate than compared to neat diesel. In like manner, stearate blend reported 3.75%, palmitate blend reported 5.73%, and oleate blend reported 6.82%, higher heat release rate than compared to neat diesel.

Relative to Biodiesel (B20) blend, oleate blend reported minimal variation in iHRR (by 5.39%), followed by palmitate blend (6.41%) and stearate blend (8.12%), respectively. From above comparison, it was evident that HRR of oleate blend remained higher owing to its unsaturation content, resulting in prolonged ID and reduced premixed combustion phase; helping the accumulated low volatile fuel to oxidize completely using its fuel bound oxygen during the diffusion combustion phase. In contrast, palmitate blend exhibited higher iHRR because of its saturation content, which required less activation energy, and minimal ID; thereby initiating early combustion and providing enough energy for the progressing combustion. Similar trend was reported for stearate blend; however, it remained lower than all other ester samples due to the reduced concentration of ethyl stearate in the diesel blend. Collectively, it can be inferred that saturated FAEs (ethyl palmitate and ethyl stearate) were responsible for the activities during the premixed combustion phase, especially the early ignition of WaFO biodiesel. Following this, unsaturated FAEs (ethyl oleate) were found to be playing crucial role in enhancing the overall HRR through their

**Figure 2.** *Instantaneous heat release rate of WaFO B20 blend and ester samples.*

delayed combustion during diffusion combustion phase, thereby liberating high amount of heat energy. Like Pmax, HRR also increased with engine load for both blend and ester samples, considering the increasing amount of fuel combusted, in order to meet the energy demand of the engine.

### *4.1.3 Ignition delay (ID)*

Ignition delay of the fuel signifies the delay period noted between the SOI and SOC; and is always represented in terms of crank shaft angle. From **Table 3** and **Figure 3**, both blend and ester samples reported reduced ID due to their high cetane number; and played a significant role in initiating the combustion well before the neat diesel. As a matter of fact, this ID is widely influenced by both physical and chemical delay; but is predominantly influenced by chemical delay [40]. Accordingly, variation in ID between neat diesel and B10 blend, B20 blend and B30 blend were found to be 2.4°, 3° and 3.6° CA BTDC, lower than the former. In the same manner, variation in ID between neat diesel and oleate, stearate and palmitate blend were reported to be 0.4°, 1° and 1.2° CA BTDC, lower than the diesel sample.

Amongst ester samples compared with B20 biodiesel blend, oleate blend reported 2.6° CA BTDC, stearate blend reported 2° CA BTDC, and palmitate blend reported 1.8° CA BTDC, higher ID. It follows that, both palmitate and stearate blends exhibited shortened ID owing to their higher cetane number because of their higher saturation. Yet, higher delay period than B20 (biodiesel) blend was explained by the reduced availability of ethyl palmitate and ethyl stearate in their blend samples. On contrary, oleate blend reported longer ID than other ester samples due to their low cetane number, accounting its unsaturation and increased availability; besides its high viscosity. Eventually, WaFO biodiesel reported shortened ID because of its saturated

**Figure 3.** *Ignition delay of WaFO B20 blend and ester samples.*

FAEs (ethyl palmitate and ethyl stearate) which exhibited early SOC, and initiated the combustion of their unsaturated counterparts. Adding to this, the unsaturated FAEs (ethyl oleate) themselves had higher CN than diesel, which allowed it to initiate early SOC. Here, ID of test samples reduced with increasing engine load, citing the increased availability of fuel. Especially, both blend and ester samples reported lower ID in view of more amount of fuel injected, which indirectly signified increased cetane number.

#### **4.2 Performance characteristics**

#### *4.2.1 Specific fuel consumption (SFC)*

In general, Specific fuel consumption reports about the fuel requirement of the engine, for producing 1 unit of power [41, 42]. From **Table 3** and **Figure 4**, it can be noted that diesel sample reported lowest SFC amongst all test samples owing to its superior calorific value, and low density. As well, absence of long to very long carbon chained molecules in the diesel simply reduced its viscosity, which enhanced its rate of atomization and vaporization. Supporting this, B10 blend reported 18.77%, B20 blend reported 23.20% and B30 blend reported 29.87%, higher SFC than neat diesel; whereas, ester samples reported higher SFC by 5.8%, 9.66%, 13.67% for stearate blend, palmitate blend and oleate blend, respectively.

In comparison with B20 (biodiesel) blend, oleate blend reported 7.71%, palmitate blend reported 10.97%, and stearate blend reported 14.10%, lower SFC. Here, oleate blend reported highest SFC amongst other ester samples owing to its unsaturation, resulting in reduced calorific value, which demanded more fuel to meet the energy equivalence demand. Besides, increased density and kinematic viscosity favored poor

**Figure 4.** *Specific fuel consumption rate of WaFO B20 blend and ester samples.*
