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

atomization and vaporization, thereby leading to poor combustion; and again demanded surplus fuel to satisfy the energy demand. Meanwhile, both stearate blend and palmitate blend reported low SFC due to their slightly higher calorific value, which helped in deriving maximum heat energy output. Inspite of long carbon chains contributing to their increased density and viscosity, these samples reported low rate of fuel consumption citing their reduced availability in the blend sample and superior calorific value of diesel, itself. Summing up, both saturated (ethyl palmitate and ethyl stearate), and unsaturated FAEs (ethyl oleate) are responsible for the increased SFC of WaFO biodiesel, accounting their long carbon chains. Also, unsaturation in the WaFO biodiesel had negative impact on its overall calorific value, thus consuming more fuel to produce the equivalent work. Oddly, trend of SFC curve reduced with increasing engine load for all test samples, suggesting that the brake power increased along with engine load [43].

## *4.2.2 Brake thermal efficiency (BTE)*

In common practice, the capability of the engine to produce actual mechanical work output by converting the stored chemical energy in the fuel is signified by its brake thermal efficiency; and correlates brake power with the fuel power [32]. From **Table 3** and **Figure 5**, compared with neat diesel, lower BTE was reported for B10 blend by 10.29%, B20 blend by 13.05% and B30 blend by 15.5%; and, for stearate blend by 2.47%, palmitate blend by 4.68%, and oleate blend by 7.62%. Here, high BTE for diesel, inspite of low cetane number, was explained by its superior calorific value and low volatility, which allowed it to undergo complete combustion especially during its diffusion combustion phase; inspite of its lack of fuel bound oxygen content [44].

**Figure 5.** *Brake thermal efficiencies of WaFO B20 blend and ester samples.*

Compared to B20 (biodiesel) blend, oleate blend reported 6.24%, palmitate blend reported 9.65%, and stearate blend reported 12.22%, higher BTE. Here, stearate blend exhibited highest BTE amidst other ester samples because of its increased calorific value; and reduced availability of ethyl stearate in the blend sample, which had a significant effect on its resultant viscosity. Moreover, shortened ID of ethyl stearate provided it sufficient time to get combusted during premixed combustion phase, and supply sufficient energy for the accumulated diesel to get combusted rapidly during the diffusion combustion phase; thereby resulting adequate amount of heat energy. Likewise, palmitate blend also reported similar phenomenon; however, reduced BTE was explained by its increased concentration than stearate blend. Unlike this, oleate blend reported lowest BTE amongst ester samples citing its unsaturation, inferior calorific value, and increased rate of viscosity; hence, requiring more amount of fuel for energy equivalence. However, higher BTE than B20 blend was explained by the reduced availability of ethyl oleate in the blend sample, and its efficacy to undergo complete oxidation using its fuel bound oxygen. Comparing these results, it can be inferred that saturated FAEs (ethyl palmitate and ethyl stearate) initiated combustion during the premixed phase, and provided sufficient activation energy for initiating the combustion of unsaturated FAEs (ethyl oleate) during the diffusion combustion phase. Besides, in view of early SOC due to shorted ID, FAEs in WaFO reported early ignition and underwent complete oxidation using its fuel bound oxygen content; thus, reporting similar BTE like neat diesel. Again, BTE of all test samples increased with engine load, considering the increasing amount of fuel combusted, in order to meet the energy demand of the engine [45].

#### **4.3 Emission characteristics**

#### *4.3.1 Carbon monoxide (CO) emission*

In general, CO emission is considered as secondary by-product during combustion; and its presence in exhaust gas signifies incomplete combustion of fuel inside engine cylinder. Infact, CO emission arises in case of poor atomization, improper air-fuel mixing, deprived oxygen content, insufficient time for completion of combustion, and even engine's operating conditions; in addition to fuel's molecular properties like unsaturation, C/H ratio, and even aromaticity [46]. From **Table 3** and **Figure 6**, both blend and ester samples reported lower CO emission against neat diesel because of their fuel bound oxygen content, which was responsible for the completion of their oxidation; and, leaving behind only a small portion of partially combusted CO emissions. Relatively, CO emission remained reduced for B10 blend by 35.66%, B20 blend by 45.76% and B30 blend by 52.04%; and, for palmitate blend by 10.52%, stearate blend by 22.31%, than compared to neat diesel. In contrast, oleate blend reported higher CO emission (by 15%), than compared to neat diesel sample.

As compared with B20 (biodiesel) blend, stearate blend reported 45.86%, palmitate blend reported 70.69%, and oleate blend reported 122.45%, higher CO emission. Here, both palmitate and stearate blends reported higher CO emissions; and was explained by their reduced availability and long carbon chained molecules, inspite of their shortened ID and fuel bound oxygen content. Furthermore, oleate blend reported highest CO emission amongst other test samples on account of its unsaturated double bond in its FA moieties [40, 47]. Besides, delayed combustion encouraged the rapid combustion of accumulated fuel during diffusion combustion phase, thereby increasing the CO concentration. Summarizing this, WaFO biodiesel reported reduced CO emission in view of its fuel bound oxygen molecules in their FAEs; yet, it *Molecular Contribution of Fatty Acid Esters in Biodiesel Fueled CI Engines DOI: http://dx.doi.org/10.5772/intechopen.102956*

**Figure 6.** *Carbon monoxide emission of WaFO B20 blend and ester samples.*

reported significant traces of CO due to its unsaturated FAEs (ethyl oleate). To be noted, saturated FAEs (ethyl palmitate and ethyl stearate) ensured complete oxidation of WaFO biodiesel by providing sufficient activation energy for its unsaturated counterparts. Again, CO emissions of both blend and ester samples increased along with engine load, and were explained by the increasing amount of fuel injected into the cylinder to meet the energy demand of the engine.
