Effect of Various Additives on Biodiesel Properties

Effect of Additives on Fuel Properties

The fuel properties of biodiesel and conventional fuel are comparable to each other and can be used together as an alternative fuel for the diesel engine. The effect on fuel properties of chicken fat methyl ester (CFME) biodiesel mixed with a magnesium based additive were examined by Guru et al. (2010). The study showed that on decreasing the dosage of additive from 16 to 0 mmoL/L in the fuel blend, a significant increment in the value of the freezing point, flash point, and viscosity were observed. Also, a change in fuel properties confirms that the catalytic cracking effect of the additive results in the break-dowm of longer chains of hydrocarbons into smaller ones.

Cao et al., (2014) conducted an experimental study on ‘waste cooking oil methyl ester’ (WCOME) blends (B20) by adding an ‘ethylene vinyl acetate copolymer" (EVAC) additive. EVAC has excellent cold flow improvers and decreases the formation of wax crystals in the fuel. The results showed considerable improvement in kinematic viscosity, oxidation stability, acid value, and the flash point of diesel-bio-diesel blends. Also, as the concentration of additive increases from 0 to 0.1 wt% in the fuel blend, the values are upgraded of the above-mentioned fuel properties, i.e. 37.9% in viscosity, 8.19% in oxidation stability, 20% in acid value, and 4.72% in the flash point were reported. Similar research on mahua oil feedstock by Bhale et al. (2009) was carried out. Ethanol and kerosene were used as an additive to the biodiesel. The authors observed that increasing the concentration of ethanol in the biodiesel and its blends showed a significant reduction in fuel viscosity as compared to neat biodiesel. This is because ethanol acts as a wax depressant and restricts the formation of wax crystals in the fuel. However, on the other hand, a significant reduction in the flash/fire point was observed on using ethanol and kerosene as fuel additives.

Scientists have also explored the potentials of biobased fuel additives in biodiesel fuel. Joshi et al. (2011) examined the variation in fuel properties, i.e. kinematic viscosity, acid value, and flash point by adding ’ethyl levulinate (ethyl 4-oxopentano-ate)’ to cottonseed oil and poultry fat biodiesel. The results showed that on increasing the concentration of additive from 0 to 20 vol% in the biodiesel, the acid values of ‘cotton seed methyl esters’ (CSME) and ‘poultry fat methyl esters’ (PFME) were not significantly affected, though increasing the dosage has shown a concomitant decrease in the value of viscosity and flash point. The addition of ethanol as a fuel additive served a dual role for neem oil biodiesel and its blends, according to a study conducted by Sivalakshmi and Balusamy (2012). The results showed a substantial reduction in the calorific value and cetane index of fuel blends. However, viscosity reduced sharply at 40°C.

Effect of Additives on Cold Flow Properties

Cold flow properties determine how effectively fuel running in the engine can withstand cold weather conditions. Due to clogging of the fuel filters and pipelines at low ambient temperatures, these parameters play a significant role, especially in the colder regions. The cold flow properties for biodiesel can be illustrated in terms of its three properties, i.e. the ‘cold filter plugging point’ (CFPP), pour point, and cloud point. Biodiesel is highly prone to low-temperature operating problems due to the presence of long-chain, saturated fatty acids (Van Gerpen and He, 2014). The flow properties of biodiesel can be improved by several means, i.e. the utilizing of a light-oil blend, reducing the pressure distillation, adding additives, and winterization (Abe et al., 2015).

Cold Filter Plugging Point (CFPP)

This is defined as the minimum temperature at which a certain volume of pure biodiesel flows out through the standard filter within a time period of 60 seconds. In other words, it is the critical property that is used to predict the minimum temperature at which fuel will flow freely throughout the filters in a diesel engine. This is important as in cold countries a high cold filter plugging point will clog up vehicular engines more easily.

Pour Point

This is the lowest temperature at which liquid fuel becomes semisolid and loses its flow characteristics. The reason behind the loss of flow characteristics is that crude oil has a large paraffin content which crystallizes on decreasing the ambient temperature and forms a matrix of wax crystals. This matrix holds a large quantity of the liquid fraction of the crude oil within it, thus preventing the flow of liquid. The upper and lower pour points may sometimes be specified in order to indicate a temperature window within which the fuel will start to flow.

Cloud Point

This is defined as the lowest temperature of the fuel at which wax shows a cloudy appearance. The presence of solidified wax in the fuel chokes the fuel line and blocks the fuel filter system and fuel injectors. This term also plays a significant role in the storage stability of biodiesel.

Much research has been done in order to improve the cold flow properties of biodiesel, including modification of the chemical or physical properties of either the oil feedstock or biodiesel product, the usage of different types of additives in the biodiesel, and blending with petroleum products, i.e. diesel and gasoline. Traditionally, petroleum diesel additives can be defined as pour point (PP) depressants or wax crystal modifiers. These additives were created in order to improve the pumping ability of the crude oil that inhibits crystalline growth by eliminating the accumulation of large-sized crystals.

Several research studies on cold flow properties have been carried out in the past. The effect of a magnesium-based additive on the pour point of biodiesel of chicken fat methyl ester was examined (Guru et al., 2010). The authors successfully identified that on increasing the concentration of an additive in the fuel blend from 0 to 16 mmol/1. the pour point was reduced to 7°C. A similar study was conducted to examine the effect of an EVAC additive on WCOME used in an unmodified diesel engine (Cao et al., 2014). The authors found that on adding 0.04 wt% of EVAC in the blend of biodiesel and diesel B20 (20 vol% biodiesel + 80 vol% diesel), there were notable reductions in the values of cold flow properties, i.e. 8°C in the cloud point, 11 °C in the CFPP, 10°C in the pour point, while compared with the neat diesel the values were 8°C in the cloud point, 10°C in the CFPP, and 10°C in the pour point, respectively. Therefore, the results confirmed that EVAC is an effective ’cold flow improver’ (CFI) for both waste-cooking-oil-derived biodiesel and its blends.

To investigate the effect of additives on the pumping and injecting of biodiesel in ‘compression ignition’ (CI) engines in cold weather, a comparative study on mahua biodiesel was carried out (Bhale et al., 2009). Different concentrations of ethanol and kerosene (at 5%, 10%, 15%, and 20%) and lubrizol 7671 (at 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, and 4%) were used. The results showed that at 20% ethanol concentration the cloud point of ‘mahua methyl ester' (MME) was reduced from 18°C to 8°C with a further reduction of up to 5°C for a 20% dosing level of kerosene. In addition to this, a reduction of 11 °C in the value of the pour point for 20% ethanol and a reduction of 15°C in the pour point value for 20% kerosene blended with biodiesel were observed. Reductions in the ‘specific heat capacity’ (CP) value by 4°C-5°C, the ‘pour point' (PP) values by 3°C-4°C, and the ‘cold filer plugging point’ (CFPP) values by 3°C, respectively, were observed when ‘ethyl levulinate’ (EL), a biobased fuel additive, was mixed with cotton seed methyl ester and poultry fat methyl ester biodiesel (Joshi et al., 2011).

Effect of various Additives on Engine Combustion, Performance, and Emission Characteristics

Effect of Additives on Combustion Characteristics

The combustion characteristics of any fuel are commonly governed by its chemical composition. One of the important combustion properties is how quickly the air-fuel mixture will ignite inside the engine within the optimum time. As the fuel ignition is a radical-driven reaction so the optimum dosage of fuel additives has a considerable impact on ignition properties, i.e. by enhancing or retarding the ability for ignition. In this section, we demonstrate the effect of using different kinds of additives on the combustion parameters of the biodiesel-diesel fuel blends inside the diesel engine.

The effect on combustion characteristics by adding a metal-based additive (Mg) in the fuel blend containing 90 vol% of diesel and 10 vol% of biodiesel (D90B10) was analyzed by Guru et al. (2010). A single cylinder four-stroke direct injection compression ignition engine was used for the analysis. The results illustrated an expeditious rise in cylinder pressure which is related to the combustion of fuel starting earlier with the use of the additive and the maximum engine cylinder gas pressure was also being slightly higher than that of neat diesel. The study also reported a significant increase in the cetane index of fuel blends with the addition of the additive. Hence, a short ignition delay was observed for BIO which gives a clear indication of a lower heat release rate in the premixed combustion as compared to diesel fuel.

The biobased additive ethanol had a notable impact on combustion characteristics of neem oil biodiesel. Sivalakshmi and Balusamy (2012) performed an experiment on a naturally aspirated, one-cylinder, four-stroke, direct injection diesel engine fueled with biodiesel derived from neem oil containing ethanol as an additive and diesel fuel. The experimental study reported that as the concentration of ethanol increases in the fuel blends, the peak pressure of the engine cylinder becomes higher. However, no significant change in ignition delay was observed for BE5 (5% ethanol in biodiesel) and BE10 blends when compared with neat biodiesel. The authors also confirmed that a negative heat release rate was observed due to the vaporization of the fuel that occurred at the beginning during the ignition delay. Increasing the quantity of ethanol in the fuel blend leads to the accumulation of the fuel during the premixed combustion stage, thereby resulting in higher rates of heat release for BE5 and BE 10 blends. Further increasing the ethanol content in the fuel blend leads to a higher delay in ignition than that for neat biodiesel.

Apart from the analysis done on single cylinder diesel engines, Kivevele et al. (2011) successfully tested a four-cylinder ‘turbocharged direct injection diesel engine’ in order to find out the effect of using antioxidant additives, namely ‘2-tert butyl-4-methoxy phenol’ (‘butylated hydroxyanisole’, BHA), ‘3, 4, 5-tri hydroxybenzoic acid’ (‘propyl gallate’, PG), and ‘1, 2, 3 tri-hydroxy benzene’ (pyrogallol, PY) in biodiesel derived from croton megalocarpus oil. The results revealed that in ideal conditions, no major change in the value of the peak pressure was observed with the addition of additives in the fuel blend as compared to neat diesel. However, at higher loads, the peak pressure recorded a higher value for fuel blends containing additives.

Moreover, the addition of additives in the B20 fuel blend showed a maximum rise in the peak of the heat release rate as compared to the other test fuels. Musthafa et al. (2018) carried out an experiment on a single-cylinder, four-stroke, water-cooled compression ignition engine fueled with a blend of palm-oil-derived biodiesel, ‘di-tert-butyl peroxide’ (DTBP). a cetane index improver additive at 1 vol%, and a mineral diesel in order to find out the effect of additives on the combustion phenomenon occurring inside the engine cylinder. The results showed that the maximum engine cylinder pressure was reduced when the additive is mixed in the B20 blend as compared to mineral diesel fuel. Similarly, the heat release rate was also at a maximum when the additive was added in the fuel blend as compared to the DI00 (neat diesel).

Effect of Additives on Engine Performance Characteristics

Many research studies have been carried out in the past on a wide variety of biodiesel feedstocks by incorporating different kinds of additives in order to improve the performance and emissions characteristics of C.I. engines. However, the sample of suitable additives should be chosen wisely. In this section, a comprehensive overview on the effects of amalgamating different kinds of additives on engine performance is presented.

The investigation carried out on utilizing the assets of Mg additives in fuel blends containing BIO (10% biodiesel derived from chicken fat and 90% diesel) revealed a negligible change in the value of the torque of a single-cylinder ‘direct injection’ (DI) diesel engine (Guru et al., 2010). The dosage of the additive used for doped in the biodiesel has a concentration of about 12pmol. However, a significant reduction in the brake specific fuel consumption and engine exhaust gas temperature was observed. Similarly, engine performance was analyzed by Bhale et al. (2009) on a four-stroke water-cooled single-cylinder diesel engine. The blends of MME, ethanol, and diesel in different proportions were used for the investigation. The results showed substantial improvement in engine performance at full load for an MME-ethanol-diesel blend as compared to neat diesel.

Sathiyamoorthi and Sankaranarayanan (2016) performed an experiment on a ‘common rail direct injection’ (CRDI) compression ignition (DICI) engine using biodiesel derived from lemongrass oil. BHA and BHT were used as antioxidant additives for the analysis. The authors found that on increasing the amount of BHA in the fuel blend LGO25 (25% lemongrass-oil-derived biodiesel + 75% diesel), the brake specific fuel consumption (BSFC) value was reduced significantly. An almost similar trend of BSFC was observed in the case of adding a BHT additive to the fuel blend. Also, a rise in the curve of the brake thermal efficiency trend was observed when increasing the content of antioxidant additives in LGO25.

The effect of a fuel stabilizing additive, namely acetone, on the performance of a HATZ two-cylinder ‘direct injection’ (DI) diesel engine, fueled with diesel and biodiesel derived from castor oil by adding recycled ‘expanded polystyrene’ (EPS), was successfully examined by Calder et al. (2018). The results showed that, at all engine conditions, a higher concentration of biodiesel with EPS and acetone has a better ‘brake specific energy consumption’ (BSEC) than petroleum-derived diesel fuel. Also, for all blends of biodiesel, EPS and acetone showed higher BTEs than diesel. Therefore, the highest value of BTE was recorded for B50 (50% castor oil biodiesel + 50% diesel) with EPS and acetone additives.

Effect of Additives on Exhaust Emission Characteristics

The emissions associated with the combustion processes are increasing enormously due to the global rise in transportation and energy systems (Abdel-Rahman, 1998).

Controlling emissions levels has been the prime objective of the enormous quantity of research studies and developments carried out all over the world. In this section, a survey of the previous literature on the impact of various additives on engine emissions is presented in detail.

Guru et al. (2010) investigated the effects of an organic-based synthetic Mg additive with biodiesel derived from chicken fat and a diesel blend B10 in a one-cylinder direct injection diesel engine. The results showed that doping of about 12 pmol of an Mg additive in the fuel blend results in an increase of NOx emissions by 5%. However, other harmful emissions such as CO and HC were reduced by about 13%. The utilization of a 10 vol% of ethanol additives in mahua oil biodiesel results in a significant reduction in CO, HC, and NOX emissions as compared to neat biodiesel (Bhale et al., 2009). However, with a further rise in the ethanol concentration, the emissions were found to be higher.

A similar investigation was conducted on biobased derived additive ethanol by Sivalakshmi and Balusamy (2012). The blends of neem oil biodiesel and diesel were used for analyzing the exhaust emission characteristics. The NOX emissions were found to be initially higher, with the addition of ethanol in the fuel blend. However, above a certain limit, the NOx emissions showed a decreasing trend with respect to higher loads. Moreover, at a higher ethanol concentration, CO and HC emissions were found to be higher for the diesel-biodiesel blends as compared to neat diesel.

Sathiyamoorthi and Sankaranarayanan (2016) examined the effect of antioxidant additives on the emission characteristics of an LGO25 fuel blend. The results showed that CO emissions were increased by 5.8% at 500 ppm, 10.1% at 1,000 ppm, and 14.8% at 2,000 ppm with the addition of a BHA antioxidant in an LGO25 fuel blend. Similarly, for a BHT antioxidant additive, the CO emissions were increased by 8.5% at 500 ppm, 13.2% at 1,000 ppm, and 16.60% at 2,000 ppm at full load conditions. This can be justified by the decrease in ignition delay of fuel blends with the addition of antioxidant additives and thereby encouraging the formation of CO emissions. A similar trend is observed for unburned hydrocarbon emissions, which were also found to be slightly higher with the adding of the antioxidants in the LGO25 fuel blend. However, the percentage of NOx emissions were slightly lower due to the usage of antioxidant additives.

The effect of a hybrid additive on engine emissions was successfully tested by Calder et al. (2018). The authors observed that, on adding EPS in a canola oil-biodiesel fuel blend with or without using acetone additive showed about 20%-30% less NOx emissions as compared to that of the diesel fuel. The logic behind the decreasing NOx emissions was the lower heating value of the fuel blend in the study. The acetone was used as a stabilizer in the fuel blends. Its presence decreases the calorific value and increases the viscosity which results in the poor atomization of the fuel blends at low engine speed. The results also illustrated that EPS dissolved in B50 blends with or without using acetone generates more smoke emissions as compared to diesel. Moreover, acetone added to B20 and B50 blends showed a reduction of about 58% in CO emissions as compared to neat diesel. Table 14.2 summarizes the effect of using different kinds of additives on engine combustion, performance, and emissions of biodiesel and its blends under various engine operating conditions.

TABLE 14.2

Variation in Engine Characteristics of Different Biodiesel Fuel by the Addition of Additives of Different Concentration

Additive

Peak

Biodiesel

Additive

Concentration

Engine Specification

RPM HRR

Pressure HC

CFME (B10) Mg

12 pmol

Air-cooled DI engine, 18:1. 1-cylinder

2200 (at full load A

condition) '

t -

MME

Ethanol

20 vol%

1-cylinder. water-cooled, 17.5:1

1500 (at different — loading condition)

- t

NOME

Ethanol

5-10 vol%

Single-cylinder DI engine.

16.5:1

1500 (at various A

loading '

conditions)

t t

LGO

BHA

BHT

  • 500-2000 ppm
  • 500-2000 ppm

Single cylinder. DI. air cooled. 17.5:1

1500 —

- t f

COME” + EPS

Acetone

50 tnl/L

Twin cylinder air-cooled, 20.5:1

1000-3000 (at —

various loading conditions)

COME"

PY

1000 ppm

TDI, 19.5:1

3000 (at various — loading conditions)

— —

POME

HOME

DTBP

Alumina

nanoparticle

  • 1 vol%
  • 20-60 ppm

Single cylinder, water-cooled. 14:1-18:1

  • 1500 |
  • 1500

1 t t ;

JOME

MWCNT

10-50 ppm

1-cylinder. DI. air-cooled

1500-2500

t i

MOME

TiO,

100-200 ppm

1-cylinder. DI. air-cooled

1100 (at different A

loading '

conditions)

t i

CO NOx BP BTE

I t I

I ; t

'it At higher dose)

t I t

t I t

I I

t t

I I

I t

I I

I I

References

I Guru et al. (2010)

I Bhale et al. (2009)

tSivalakshmi and

Balusamy (2012)

▲ Sathiyamoorthi and ' Sankaranarayanan

f (2016)

▲ Calder et al. (2018)

tKivevele et al.

(2011)

tMusthafa et al.

(2018)

t Abdel-Rahman

(1998)

▲ El-Seesy et al.

T (2017)

  • —s Yuvarajan et al.
  • (2017)

CFME = chicken fat methyl ester. MME = mahua methyl ester. NOME = neem oil methyl ester. LGO = lemongrass oil. COME’ = canola oil methyl ester. EPS = expanded polystyrene. COMEh = croton oil methyl ester. POME = palm oil methyl ester. HOME = honge oil methyl ester. Mg = magnesium. BHA = butylated hydroxyanisole. BHT = butylated hydroxytoluene. PY = pyrogallol. DTBP = di-tert-butyl peroxide. JOME = jojoba oil methyl ester. MOME = mustard oil methyl ester. MWCNT = multi-walled carbon nanotubes. TiO, = titanium dioxide, DI = direct injection.

294 Biodiesel Fuels

 
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