**3. Results**

Experimental results obtained with WCO blends are shown and discussed with the aim of highlighting the characteristics of performance (torque, brake specific fuel consumption, brake thermal efficiency) and pollutant emissions (NO<sup>x</sup> , CO, CO2 , HC, soot concentration, particle number concentration, particle size distributions).

**Figure 2** shows the variation of engine torque with speed at full-load condition for diesel fuel, B20, and B40. The torque trend at full-load condition depends on the percentage of biodiesel in the fuel; since WCO has a lowering heating value than ULSD, the engine torque values related to B40 are the lowest at all engine speeds.

In order to allow the comparison between data obtained for the different fuels, it was established to perform tests at 80% of full load evaluated using diesel fuel, so as to impose the same value of load to the engine for all tested fuels.

**Figure 3** shows the variation of brake specific fuel consumption (BSFC) with engine speed for 100% load. The fuel consumption increases with the content of WCO in the fuel. This is to attribute to the reduction in energy content in the biodiesel as regards diesel fuel. The average increase in BSFC over all engine speed values is 3.9% for B20 and 7.1% for B40.

Brake thermal efficiency (BTE) versus engine speed is plotted in **Figure 4**. It was evaluated by computing the ratio of the brake power to the power provided by the consumed fuel at full-load condition. The differences in the B20 and B40 averaged values are only about 1% as compared to diesel fuel.

Exhaust temperature is a very important indicator of the combustion process and has a key role in the formation of pollutants. **Figure 5** presents the variation of exhaust temperature with engine speed obtained with ULSD, B20 and B40 at 80% of load. The thermocouple was placed just downstream junction of the two-branches that connects the cylinders to the exhaust duct. All fuels are characterized by an increase of temperature with engine speed. The trends show a reduction in exhaust temperature with the increase in biodiesel ratio in the blend. This behavior

is ascribed to the lower heating value of biodiesel, which reduces the amount of total energy released, thus reducing the combustion peak temperature and then the exhaust temperature. Data from literature are contradictory: some authors report that biodiesel has a higher combustion temperature as regards diesel fuel [13]; other authors assert the opposite behavior [23].

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**Figure 3.** Variation of brake specific fuel consumption with engine speed [31].

**Figure 2.** Variation of engine torque with engine speed [31].

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**Figure 2.** Variation of engine torque with engine speed [31].

The data acquisition started after the engine warm-up in order to let the engine reach nominally stationary conditions. For each running condition, 25 engine cycles were used to average the signal, thus to attenuate the engine cycle irregularities (the increase in this number did not

Experimental results obtained with WCO blends are shown and discussed with the aim of highlighting the characteristics of performance (torque, brake specific fuel consumption,

**Figure 2** shows the variation of engine torque with speed at full-load condition for diesel fuel, B20, and B40. The torque trend at full-load condition depends on the percentage of biodiesel in the fuel; since WCO has a lowering heating value than ULSD, the engine torque values

In order to allow the comparison between data obtained for the different fuels, it was established to perform tests at 80% of full load evaluated using diesel fuel, so as to impose the same

**Figure 3** shows the variation of brake specific fuel consumption (BSFC) with engine speed for 100% load. The fuel consumption increases with the content of WCO in the fuel. This is to attribute to the reduction in energy content in the biodiesel as regards diesel fuel. The average

Brake thermal efficiency (BTE) versus engine speed is plotted in **Figure 4**. It was evaluated by computing the ratio of the brake power to the power provided by the consumed fuel at full-load condition. The differences in the B20 and B40 averaged values are only about 1% as

Exhaust temperature is a very important indicator of the combustion process and has a key role in the formation of pollutants. **Figure 5** presents the variation of exhaust temperature with engine speed obtained with ULSD, B20 and B40 at 80% of load. The thermocouple was placed just downstream junction of the two-branches that connects the cylinders to the exhaust duct. All fuels are characterized by an increase of temperature with engine speed. The trends show a reduction in exhaust temperature with the increase in biodiesel ratio in the blend. This behavior

increase in BSFC over all engine speed values is 3.9% for B20 and 7.1% for B40.

, CO, CO2

, HC, soot concentration,

change the feature of the trends).

**Table 3.** Biodiesel composition.

brake thermal efficiency) and pollutant emissions (NO<sup>x</sup>

**Mass fraction Biodiesel** Carbon 0.812 Hydrogen 0.065 Oxygen 0.117 Sulfur 0.006

24 Improvement Trends for Internal Combustion Engines

related to B40 are the lowest at all engine speeds.

value of load to the engine for all tested fuels.

compared to diesel fuel.

particle number concentration, particle size distributions).

**3. Results**

**Figure 3.** Variation of brake specific fuel consumption with engine speed [31].

is ascribed to the lower heating value of biodiesel, which reduces the amount of total energy released, thus reducing the combustion peak temperature and then the exhaust temperature. Data from literature are contradictory: some authors report that biodiesel has a higher combustion temperature as regards diesel fuel [13]; other authors assert the opposite behavior [23].

**Figure 6** shows the variation of NO<sup>x</sup>

literature [7, 33].

lished data [7, 18].

**Figure 6.** Variation of NO<sup>x</sup>

emission with engine speed [31].

CO2

emission with engine speed at a fixed value of load con-

Effect of Waste Cooking Oil Biodiesel Blends on Performance and Emissions...

with the

27

, which is evident for

emission can be explained by consider-

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dition (80%). It is expressed as NO equivalent. All fuels exhibit a decrease in NO<sup>x</sup>

exhibit remarkable differences; B40 shows the greatest increase in NO<sup>x</sup>

delay that affect the duration of premixed and diffusion burn regimes [4, 9, 19].

values greater than 3000 rpm. Such increase in NO<sup>x</sup>

increase in engine speed, in agreement with literature [32]. This trend is due to the increase in the gas motion in the cylinder at higher engine speed that is responsible for a faster mixing between fuel and air and a shorter ignition delay. At higher engine speed, the residence time of high temperature within the cylinder is shortened and this causes a reduction in NO<sup>x</sup> emission, in spite of the temperature trends shown in **Figure 5**. The traces in **Figure 6** do not

ing the effect of temperature, the differences in fuel chemistry, spray properties, and ignition

In **Figure 7**, CO emission trends obtained at 80% load are shown. The oxygen content in the biodiesel blends enhances the mixing process between air and fuel, thus allowing a reduction in CO emissions for B20 and B40 as regards diesel fuel, in agreement with results from

**Figure 8** presents the variation of HC emission with respect to the engine speed. The WCO content in the blend causes a reduction in emissions as regards diesel fuel, according to pub-

 emission trends are shown in **Figure 9**. Similar behavior has been obtained for all tested fuels. The literature reports contradictory results in this field. Some authors [34] obtained

**Figure 4.** Variation of brake thermal efficiency with engine speed [31].

**Figure 5.** Variation of exhaust temperature with engine speed [31].

**Figure 6** shows the variation of NO<sup>x</sup> emission with engine speed at a fixed value of load condition (80%). It is expressed as NO equivalent. All fuels exhibit a decrease in NO<sup>x</sup> with the increase in engine speed, in agreement with literature [32]. This trend is due to the increase in the gas motion in the cylinder at higher engine speed that is responsible for a faster mixing between fuel and air and a shorter ignition delay. At higher engine speed, the residence time of high temperature within the cylinder is shortened and this causes a reduction in NO<sup>x</sup> emission, in spite of the temperature trends shown in **Figure 5**. The traces in **Figure 6** do not exhibit remarkable differences; B40 shows the greatest increase in NO<sup>x</sup> , which is evident for values greater than 3000 rpm. Such increase in NO<sup>x</sup> emission can be explained by considering the effect of temperature, the differences in fuel chemistry, spray properties, and ignition delay that affect the duration of premixed and diffusion burn regimes [4, 9, 19].

In **Figure 7**, CO emission trends obtained at 80% load are shown. The oxygen content in the biodiesel blends enhances the mixing process between air and fuel, thus allowing a reduction in CO emissions for B20 and B40 as regards diesel fuel, in agreement with results from literature [7, 33].

**Figure 8** presents the variation of HC emission with respect to the engine speed. The WCO content in the blend causes a reduction in emissions as regards diesel fuel, according to published data [7, 18].

CO2 emission trends are shown in **Figure 9**. Similar behavior has been obtained for all tested fuels. The literature reports contradictory results in this field. Some authors [34] obtained

**Figure 6.** Variation of NO<sup>x</sup> emission with engine speed [31].

**Figure 4.** Variation of brake thermal efficiency with engine speed [31].

26 Improvement Trends for Internal Combustion Engines

**Figure 5.** Variation of exhaust temperature with engine speed [31].

**Figure 7.** Variation of CO emission with engine speed [31].

The following figures are devoted to analyze how the WCO content in the fuel affects the particle emission of the engine. **Figure 10** shows the nonvolatile particle number concentration (PNC) in the exhaust (all data have been normalized by the corresponding available engine output value). Each point is a cumulative value of particles in the range 23 nm–2.5 µm. The left-hand-side plot shows the variation of PNC with the engine speed at a fixed value of load (80%). The right-hand-side plot shows the effect of load condition at a fixed value of engine speed (3300 rpm). The traces highlight the reduction in soot emission obtained with B20 as regards diesel fuel. The increase in WCO ratio in the blend causes a further decrease in PNC. The obtained results are explained by accounting for many aspects. The higher density and viscosity of WCO blends as regards diesel oil are responsible for a variation of the injection process (smaller spray angle, larger droplet size, and fuel penetration length). Studies [12, 28] report that the injection setting has also a significant role in particle emission. Furthermore, the higher cetane number of WCO as regards diesel fuel causes a reduction in ignition delay and an increase in the mixing-controlled combustion duration. The higher oxygen content of biodiesel as regards ULSD promotes the combustion process and favors

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29

emission with engine speed [31].

**Figure 11** shows the effect of engine speed and load on soot concentration in the engine exhaust. The plots highlight the increase in the values as the engine speed increases for all tested fuels. Such a behavior is in agreement with similar results from literature [5, 19], and it is due to the concurrence aspects that have to be taken into account: a reduced time for air-mixing and combustion that penalizes the mixture uniformity and the combustion completeness. In addition, the increase in engine speed is responsible for an enhancement of the

turbulence, which promotes the extent of complete combustion.

soot oxidation.

**Figure 9.** Variation of CO2

**Figure 8.** Variation of HC emission with engine speed [31].

an increase in CO2 emission for biodiesel probably due to the higher density of biodiesel in comparison with diesel fuel, that increases the overall mass. Some studies [5, 23] report the opposite behavior as a consequence of the lower carbon to hydrogen ratio and the increase in oxygen content in the biodiesel blend.

**Figure 9.** Variation of CO2 emission with engine speed [31].

an increase in CO2

oxygen content in the biodiesel blend.

**Figure 8.** Variation of HC emission with engine speed [31].

**Figure 7.** Variation of CO emission with engine speed [31].

28 Improvement Trends for Internal Combustion Engines

emission for biodiesel probably due to the higher density of biodiesel in

comparison with diesel fuel, that increases the overall mass. Some studies [5, 23] report the opposite behavior as a consequence of the lower carbon to hydrogen ratio and the increase in The following figures are devoted to analyze how the WCO content in the fuel affects the particle emission of the engine. **Figure 10** shows the nonvolatile particle number concentration (PNC) in the exhaust (all data have been normalized by the corresponding available engine output value). Each point is a cumulative value of particles in the range 23 nm–2.5 µm. The left-hand-side plot shows the variation of PNC with the engine speed at a fixed value of load (80%). The right-hand-side plot shows the effect of load condition at a fixed value of engine speed (3300 rpm). The traces highlight the reduction in soot emission obtained with B20 as regards diesel fuel. The increase in WCO ratio in the blend causes a further decrease in PNC. The obtained results are explained by accounting for many aspects. The higher density and viscosity of WCO blends as regards diesel oil are responsible for a variation of the injection process (smaller spray angle, larger droplet size, and fuel penetration length). Studies [12, 28] report that the injection setting has also a significant role in particle emission. Furthermore, the higher cetane number of WCO as regards diesel fuel causes a reduction in ignition delay and an increase in the mixing-controlled combustion duration. The higher oxygen content of biodiesel as regards ULSD promotes the combustion process and favors soot oxidation.

**Figure 11** shows the effect of engine speed and load on soot concentration in the engine exhaust. The plots highlight the increase in the values as the engine speed increases for all tested fuels. Such a behavior is in agreement with similar results from literature [5, 19], and it is due to the concurrence aspects that have to be taken into account: a reduced time for air-mixing and combustion that penalizes the mixture uniformity and the combustion completeness. In addition, the increase in engine speed is responsible for an enhancement of the turbulence, which promotes the extent of complete combustion.

**Figure 10.** a): Particle number concentration at 80% load; b): particle number concentration at 3300 rpm [35].

**Figure 11.** a): Soot concentration at 80% load, b): soot concentration at 3300 rpm [35].

The content of biodiesel in the fuel is responsible for a reduced particulate emission. This effect is ascribed to the increase in oxygen content in the blends that is responsible for a more complete combustion process and further oxidation of the already formed soot, according to Refs. [4–6, 8, 14, 19].

**Figures 12**–**14** present the effect of blend ratio on the distribution of soot particles' diameters obtained during tests in which the engine was fuelled with ULSD, B20, and B40, respectively. In all plots, the data are expressed as size spectral density (dN/dlogDp/cc). The left-hand-side plots show the variation of particle size obtained during tests in which the engine speed was varied at a fixed load condition (80%). The right-hand-side plots show the variation of particle size obtained during tests in which the load condition was varied at a fixed engine speed value (3300 rpm).

All trends exhibit a bimodal distribution of the particle size: 'nucleation' mode is comprised primarily of condensed volatile materials, mainly sulfate and heavy hydrocarbons, with particle sizes that are typically less than 30 nm; 'accumulation' mode is comprised mainly of carbonaceous particles of sizes larger than 30 nm [36]. The engine type, the operation condition, and the dilution needed prior sampling deeply affect the particle size distribution [4, 24].

diameter larger than 100 nm decreases; the number of particles of diameter lower than 100 nm increases. Load condition affects the particle size distribution; load increase causes a greater

**Figure 14.** a): Particle number concentration at 80% load for B40, b): particle number concentration at 3300 rpm for B40 [35].

**Figure 13.** a): Particle number concentration at 80% load for B20, b): particle number concentration at 3300 rpm for B20 [35].

**Figure 12.** a): Particle number concentration at 80% load for ULSD, b): particle number concentration at 3300 rpm for

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31

**Figures 13** and **14** show the data obtained with B20 and B40, respectively. The engine operative conditions affect the particle size distribution. B20 traces agree with those related to diesel fuel; the increase in engine speed causes a decrease in soot particle concentration with diameters

number of larger particles, in agreement with Ref. [14].

ULSD [35].

The graphs highlight that accumulation mode dominates in all tested conditions. ULSD shows a decrease in particle diameters as engine speed increases: the number of particles of Effect of Waste Cooking Oil Biodiesel Blends on Performance and Emissions... http://dx.doi.org/10.5772/intechopen.69740 31

**Figure 12.** a): Particle number concentration at 80% load for ULSD, b): particle number concentration at 3300 rpm for ULSD [35].

**Figure 13.** a): Particle number concentration at 80% load for B20, b): particle number concentration at 3300 rpm for B20 [35].

The content of biodiesel in the fuel is responsible for a reduced particulate emission. This effect is ascribed to the increase in oxygen content in the blends that is responsible for a more complete combustion process and further oxidation of the already formed soot, according to

**Figure 10.** a): Particle number concentration at 80% load; b): particle number concentration at 3300 rpm [35].

**Figure 11.** a): Soot concentration at 80% load, b): soot concentration at 3300 rpm [35].

**Figures 12**–**14** present the effect of blend ratio on the distribution of soot particles' diameters obtained during tests in which the engine was fuelled with ULSD, B20, and B40, respectively. In all plots, the data are expressed as size spectral density (dN/dlogDp/cc). The left-hand-side plots show the variation of particle size obtained during tests in which the engine speed was varied at a fixed load condition (80%). The right-hand-side plots show the variation of particle size obtained during tests in which the load condition was varied at a fixed engine speed

All trends exhibit a bimodal distribution of the particle size: 'nucleation' mode is comprised primarily of condensed volatile materials, mainly sulfate and heavy hydrocarbons, with particle sizes that are typically less than 30 nm; 'accumulation' mode is comprised mainly of carbonaceous particles of sizes larger than 30 nm [36]. The engine type, the operation condition, and the dilution needed prior sampling deeply affect the particle size distribution [4, 24]. The graphs highlight that accumulation mode dominates in all tested conditions. ULSD shows a decrease in particle diameters as engine speed increases: the number of particles of

Refs. [4–6, 8, 14, 19].

30 Improvement Trends for Internal Combustion Engines

value (3300 rpm).

**Figure 14.** a): Particle number concentration at 80% load for B40, b): particle number concentration at 3300 rpm for B40 [35].

diameter larger than 100 nm decreases; the number of particles of diameter lower than 100 nm increases. Load condition affects the particle size distribution; load increase causes a greater number of larger particles, in agreement with Ref. [14].

**Figures 13** and **14** show the data obtained with B20 and B40, respectively. The engine operative conditions affect the particle size distribution. B20 traces agree with those related to diesel fuel; the increase in engine speed causes a decrease in soot particle concentration with diameters

For what concerns the exhaust emissions, a reduction in CO and HC was observed for bio-

Effect of Waste Cooking Oil Biodiesel Blends on Performance and Emissions...

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A reduction in particulate emissions was attained for WCO blends, along with a correspond-

Particle size distributions were characterized by a bimodal distribution, in which accumulation mode dominated. A slight reduction in the particulate number concentration was observed as compared to diesel oil. The reduction was more evident as the WCO content in the fuel increased. The mean size of particles in B20 and B40 was smaller than that obtained with ULSD. For all fuel, engine load and speed conditions affected the particle size distribution: the increase in engine speed was responsible for a reduction in particles' diameters; the

We acknowledge the fundamental contribution of AVL which provided the instrumentation for the particle matter measurements (AVL Particle Counter and AVL Micro Soot Sensor) used

, according to the well-known trade-off between NO<sup>x</sup>

and particulate.

33

diesel blends, which was more significant with the increase in WCO in the fuel.

increase in load led to a reduction in the number of smaller particles.

ing increase in NO<sup>x</sup>

**Acknowledgements**

during the research activity.

**Nomenclature**

**Author details**

Giancarlo Chiatti\*, Ornella Chiavola and Erasmo Recco

PNC nonvolatile particle number concentration

B20 80% ULSD and 20% WCO, by volume B40 60% ULSD and 40% WCO, by volume BSFC brake specific fuel consumption

BTE brake thermal efficiency CMD count mean diameter D<sup>p</sup> particle diameter FFA free fatty acids

ULSD ultralow-sulfur diesel WCO waste cooking oil

\*Address all correspondence to: ornella.chiavola@uniroma3.it Engineering Department, 'ROMA TRE' University, Rome, Italy

**Figure 15.** a): Accumulation mean diameter at 80% load, b): accumulation mean diameter at 3300 rpm [35].

larger than 100 nm. B40 trends show that the increase in engine speed is responsible for an increase in the concentration of particles of diameters under 100 nm and larger than 200 nm. The traces highlight the abrupt decrease in particle number concentration in the range of diameters around 1 µm. The increase in load (at constant engine speed) is responsible for the increase in particles' sizes for both B20 and B40.

The comparison between the particles' distributions points out that B20 and B40 are characterized by lower number of particles than ULSD in almost all diameters. This behavior agrees with literature data. Studies report that the employment of biodiesel blends produces an increased number of nanoparticles and a reduced number of ultrafine and fine particles in comparison with ULSD [6, 37, 38]. It can be explained by the oxygen content of WCO that favors the combustion completeness in the region of fuel-rich diffusion flame and then promotes the oxidation of the already-formed soot and inhibits the soot growth [19].

In **Figure 15**, the variation with engine operative conditions of the mean size of accumulation mode is shown. For all tested fuels, the court mean diameter decreases with increasing engine speed at constant load value. The increase in load condition causes an increase in the court mean diameter.

WCO biodiesel blends have lower mean diameter in their exhaust than diesel fuel. B40 has smaller particle mean diameter as regards B20 for almost all tested conditions.
