An Experimental Investigation of Unregulated Pollutants from a Multi-Cylinder Diesel Engine: Impact of Ethanol Blending on Aldehyde Emissions

Unregulated gaseous exhaust emissions include substances that are poisonous, carcinogenic, or act as precursors to secondary pollutants including the creation of ozone and secondary organic aerosols (SOA). Currently, unregulated emissions are not subject to government legislations. However, as the percentage of blending is increased, an increase in emissions of carbonyl compounds is expected. There are 15 such carbonyl compounds which are categorically designated as un-regulated emissions, and are listed in Table 1.

Of these, formaldehyde and acetaldehyde are particularly harmful substances. Formaldehyde has been classified as "carcinogenic to humans" by the International Agency for Research on Cancer (IARC), while acetaldehyde is classified as a possible human carcinogen (group 2B) by the same agency. Formaldehyde is absorbed through the skin and ingestion can lead to corrosive injuries in the gastrointestinal tract. On the other hand, acetaldehyde can cause dermatitis upon skin contact and has detrimental effects on the central nervous system when inhaled [4].

Table 1. List of carbonyl compounds [5]

Diesel engines are known for their reliability, dependability and efficiency. Unfortunately, they are also significant sources of pollution. While it is difficult to reduce the levels of noxious combustion gases in diesel engines through improvements in the combustion chamber and fuel injection process alone, it is believed that clean combustion in diesel engines can be achieved through reformulation of the fuel constituents. One way to achieve this is by adding ethanol to diesel fuel, which changes its chemical properties. With the blend of ethanol and diesel, properties such as density, cetane number, thermal efficiency, viscosity and boiling point decrease. Table 2 shows the individual fuel properties of diesel and ethanol.

Table 3 presents the key properties of the base diesel fuel (D0) and the diesel-ethanol blend (D20). The comparison reveals some notable deviations in certain fuel characteristics when ethanol is blended with diesel. Specifically, the D20 fuel, which contains 20% ethanol and 80% diesel, exhibited slight variations in properties such as Flash Point, cetane number, water content, and gross calorific value. The Flash Point of D20 was lower than that of the base diesel, indicating a reduced temperature threshold for ignition, which is typical when ethanol is blended with diesel. The cetane number, a measure of combustion quality, also showed a marginal change, potentially influencing the ignition delay in the combustion process. Additionally, an increase in water content was observed in D20 due to the hygroscopic nature of ethanol, which can absorb moisture from the atmosphere. The gross calorific value of the D20 blend was slightly reduced compared to that of base diesel, reflecting the lower energy content of ethanol. All fuel properties were measured and evaluated according to the IS1460 test standard, ensuring that the data was obtained using reliable and standardized testing procedures. These differences in fuel properties influence the engine performance, combustion characteristics, and emissions, which underscores the importance of understanding the effects of alternative fuel blends on internal combustion engines

To ensure that ethanol-blended diesel fuel exhibits the necessary physicochemical properties for optimal engine performance and fuel stability, the additive is introduced. The additive is designed to address specific challenges associated with blending ethanol and diesel, such as phase separation, poor lubricity, low cetane number, and increased corrosion potential. Because diesel is a non-polar hydrocarbon and ethanol is a polar, hygroscopic substance, their direct mixing results in immiscibility, especially under varying temperature and humidity conditions. This leads to phase separation and stratification in the fuel, adversely affecting its consistency and performance.

Table 2. Diesel-ethanol properties

Table 3. Base diesel and D20 properties

In addition to stabilizing the blend, the additive also enhances other physicochemical properties of the fuel. For instance, a cetane improver is added to increase the cetane number, which is an indicator of the fuel's ignition quality and combustion characteristics. A lubricity enhancer is also included to mitigate the lower lubricity of ethanol, reducing wear on engine components. Anti-corrosion agent is used to counteract ethanol's tendency to absorb moisture, which can lead to corrosion in the fuel system. In this study, the additive was formulated carefully by selecting the appropriate chemicals.

However, the impact of ethanol on diesel fuel engine varies depending on engine operating conditions, ethanol content and the additives used. As the ethanol content increases in diesel fuel, smoke, CO₂ emissions and NO_X emissions decrease [15]. At idle and low load conditions, the blended fuel lowers smoke emissions [16]. However, unregulated compounds are expected to increase with blending.

Detailed investigations are needed to document the exact extent of the increase in unregulated emissions due to ethanol blending in diesel fuels.

In this study, emission samples were collected in the dinitrophenylhydrazine (DNPH) cartridges intergraded with the emission system of the engine test cell and the samples were analysed using high performance liquid chromatography. The carbonyl group reaction of DNPH species is shown in Figure 6. The process followed for sample collection is depicted in the form of a flow chart in Figure 7.

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Figure 6. Carbonyl group reaction with DNPH [17]

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Figure 7. Sample collection process flow chart

During the sample collection process, a consistent flow rate of 1 litre per minute (LPM) was meticulously maintained using a calibrated rotameter to ensure the accuracy and reliability of the data. The sampling was conducted over a total duration of 16 minutes, corresponding to an 8-mode test cycle, with each mode lasting for 2 minutes. This approach allowed for a comprehensive assessment of the emissions across various engine operating conditions. The samples were collected using a 2, 4-dinitrophenylhydrazine (DNPH) cartridge, which is well-suited for capturing carbonyl compounds from exhaust gases.

Quality assurance procedure:

To ensure the accuracy of the flow rate and to confirm the integrity of the sample collection system, measurements were taken at both the inlet and outlet of the sampling setup using an air flow calibrator with a range of 1 to 20 LPM. This dual-point measurement procedure was implemented to verify leak-free operation throughout the entire sampling process, thereby ensuring that the sample collection was conducted under optimal conditions. To ensure the repeatability of the process, two samples were measured (D20-S1 and D20-S2) and analyed. By maintaining a precise and stable flow rate, the study aimed to minimize measurement errors and enhance the reliability of the collected data for subsequent analysis of unregulated pollutants.

Engine dynamometers, exhaust gas analysers, exhaust gas dilution systems for particle collection, and suitable data-acquisition systems available in the laboratories to regulate and monitor the engine test runs were used for this research study.

The specifications of the engine used in this research are mentioned in Table 4. The testing was performed on a variable speed engine based on ISO 8178 C1 (8-mode) test cycle. In the initial part of the study, pure diesel (D0) was used, thereafter the diesel - ethanol blended fuel (D20) was used for the testing. Using cartridges of dinitrophenylhydrazine (DNPH), carbonyl compounds were extracted from the exhaust gases. The unregulated emission sample was collected from the same location as that of the regulated particulate samples. An acetonitrile/water solution was used to extract the DNPH derivatives. Emissions of 13 aldehydes and 2 ketones were examined using high-performance liquid chromatography (HPLC) technology. Formaldehyde and acetaldehyde emissions were specially focused due to their adverse effects. Other aldehydes analysed included acrolein, propionaldehyde, crotonaldehyde, methacrolein, butyraldehyde, benzaldehyde, valeraldehyde, m-tolualdehyde and hexanal.

Figure 8 shows the schematic layout of the experimental set-up used during the sample collection and engine testing. AVL make steady state dynamometer, Horiba make emission analyser for measurement of gas emissions like HC, CO, NOx, and CO₂ and AVL make particulate measuring system were used during the testing. The HPCL column specifications are elaborated in Table 5.

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Figure 8. Engine testing schematic diagram

Table 5. HPLC column specifications

The engine under study was initially tested neat diesel (D0) and later tested with diesel-ethanol blended fuel (D20). The testing with D20 was carried out with two identical samples designated as D20-S1 and D20-S2. Table 6 elaborates the emission values of each pollutant for D0, D20-S1 and D20-S2. In total, 15 carbonyl compounds were analyzed of which 9 components were found to be below detection limit (BDL).

The results clearly indicate that blending diesel with ethanol has a substantial impact on the levels of specific carbonyl compounds emitted in the exhaust gases. Notably, the concentrations of formaldehyde and acetaldehyde were found to increase significantly when diesel-ethanol blended fuel was used, in comparison to pure diesel fuel. The formaldehyde concentration rose by approximately 115%, suggesting that the presence of ethanol promotes the formation of this compound during combustion. Even more prominent was the increase in acetaldehyde levels, which surged by nearly 3300%, indicating a significant rise in its formation due to the introduction of ethanol into the fuel mixture. This noticeable increase can be attributed to the higher oxygen content in ethanol, which enhances the oxidation of hydrocarbons, thereby facilitating the formation of oxygenated species such as aldehydes.

Table 6. Un-regulated emission results

Conversely, the concentration of acetone in the exhaust emissions showed a clear reduction with the use of diesel-ethanol blends. Specifically, acetone levels decreased by about 88% compared to emissions from pure diesel. This significant reduction could be due to the change in the combustion characteristics in the presence of ethanol, which favors the formation of other oxygenated compounds over acetone. The changes in the levels of these carbonyl compounds highlight the complex nature of combustion chemistry when alternative fuels are used and underscore the need to understand how such blends affect the formation of various unregulated pollutants.

From these results, it is evident that the levels of formaldehyde and acetaldehyde increase significantly when diesel is blended with ethanol, as compared to diesel alone. Additionally, the levels of acetone decrease significantly with diesel-ethanol blending. Formaldehyde levels increased by approximately 115%, while acetaldehyde levels increased by almost 3300% with diesel-ethanol blended fuel when compared to pure diesel. In contrast, acetone levels decreased by 88% with diesel-ethanol blended fuel when compared to diesel.

It is important to note that these pollutants are measured in µg, which is why a substantial difference is observed. The levels of various unregulated emissions are illustrated in Figure 14 for better understanding. When all the constituents are combined, there is a 430% increase in unregulated emissions levels observed with diesel-ethanol blended fuel as compared to pure diesel.

These findings provide crucial information about how diesel-ethanol blends affect emissions. They further contribute to a more complete understanding of the impact of alternative fuels on engine exhaust composition in the context of literature published in this field.

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Figure 14. Comparison of emissions of un-regulated pollutants with different blends

The formulation of formaldehyde, acetaldehyde, and acetone is further explained in the following section for a more detailed understanding to help decide appropriate mitigation strategies.

A. Formaldehyde Formation

When diesel and ethanol are burned together, the process results in the production of formaldehyde (CH₂O) through complex chemical reactions involving both fuels. This process is described as follows:

Initial Combustion:

Diesel and ethanol are vaporized and mixed with air before ignition. During the compression stroke, the temperature and pressure rise, which initiates combustion.

Primary Combustion:

During the early phases of combustion, the hydrocarbons present in diesel fuel undergo pyrolysis and oxidation reactions, leading to the breakdown of larger hydrocarbon fragments into smaller ones. These smaller fragments react with oxygen to form carbon dioxide (CO₂) and water vapor (H₂O). Similarly, ethanol also undergoes similar combustion reactions.

Intermediate Species Formation:

In the combustion chamber, intermediate products from both diesel and ethanol combustion can react to form formaldehyde under high temperatures and pressures. These intermediate products include free radicals such as methyl (CH3) and hydroxyl (OH) radicals, which combine to create methanol (CH3OH) and hydroxymethyl (CH₂OH) radicals. These radicals then react with oxygen to produce formaldehyde.

Formaldehyde Formation:

The hydroxymethyl radicals (CH₂OH) formed from the intermediate species can undergo further reactions, such as hydrogen abstraction and oxygen addition, leading to the formation of formaldehyde (CH₂O). The reactions involved in the Formaldehydes formation are described as follows.

Oxidation of Hydrocarbons:

In the combustion of diesel and ethanol, hydrocarbons present in both fuels undergo oxidation reactions with oxygen (O₂) from the air. These reactions produce carbon dioxide (CO₂) and water vapor (H₂O) as primary combustion products.

Diesel:

$$\mathrm{C}_{\mathrm{n}} \mathrm{H}_{\mathrm{m}}+\left(\frac{\mathrm{n}}{2}+\frac{\mathrm{m}}{4}\right) \mathrm{O}_2 \rightarrow \mathrm{nCO}_2+\frac{\mathrm{m}}{2} \mathrm{H}_2 \mathrm{O}$$

Ethanol:

$$\mathrm{C}_2 \mathrm{H}_5 \mathrm{OH}+3 \mathrm{O}_2 \rightarrow 2 \mathrm{CO}_2+3 \mathrm{H}_2 \mathrm{O}$$

Formation of Methanol:

In the presence of oxygen, methyl radicals (CH₃.) are formed from hydrocarbon fragments. These radicals combine with another radical or react further to form methanol (CH₃OH):

$$\mathrm{CH}_3 .+\mathrm{OH} \rightarrow \mathrm{CH}_3 \mathrm{OH}$$

Formation of Formaldehyde:

Thereafter, methanol undergoes further oxidation reactions to produce formaldehyde. This can occur through multiple steps, including hydrogen abstraction and oxygen addition reactions.

$$\begin{gathered}

\mathrm{CH}_3 \mathrm{OH}+\mathrm{OH} \rightarrow \mathrm{CH}_2 \mathrm{OH}+\mathrm{H}_2 \mathrm{O} \\

\mathrm{CH}_2 \mathrm{OH}+\mathrm{O}_2 \rightarrow \mathrm{CH}_2 \mathrm{O}+\mathrm{H}_2 \mathrm{O}

\end{gathered}$$

It is important to note that formaldehyde formation is influenced by various factors including temperature, pressure, fuel composition, combustion efficiency, and engine design. In diesel-ethanol blends, ethanol's unique combustion properties, such as its higher oxygen content and different chemical structure compared to diesel, affects the combustion process for the formation of formaldehyde and other byproducts.

B. Acetaldehyde Formation

In the combustion process of diesel-ethanol blends, acetaldehyde (CH₃CHO) forms through several pathways, including the oxidation of ethanol and the subsequent reactions of its oxidation intermediates. A simplified overview of how acetaldehyde is formed during the combustion of diesel and ethanol together is as follows:

Ethanol Vaporization and Mixing:

In a diesel-ethanol engine, ethanol is blended with diesel fuel. During the intake stroke, the blended fuel mixture is vaporized and mixed with air in the combustion chamber.

Ignition and Combustion:

During the compression stroke, the air-fuel mixture is compressed, leading to an increase in temperature and pressure. Eventually, the mixture reaches its autoignition temperature, leading to combustion. Both diesel and ethanol undergo combustion reactions, producing heat, pressure, and various combustion intermediates.

Ethanol Combustion:

Ethanol undergoes oxidation reactions, breaking down into smaller molecules and producing various intermediates. One of the primary oxidation products of ethanol is acetaldehyde. The combustion of ethanol can be represented by the following simplified equation:

$$\mathrm{C}_2 \mathrm{H}_5 \mathrm{OH}+3 \mathrm{O}_2 \rightarrow 2 \mathrm{CH}_3 \mathrm{CHO}+3 \mathrm{H}_2 \mathrm{O}$$

This equation illustrates the conversion of ethanol (C₂H₅OH) into acetaldehyde (CH₃CHO) and water vapor (H₂O) in the presence of oxygen (O₂).

C. Acetone Formation

Acetone (CH₃COCH₃) forms in the combustion of diesel-ethanol blends through various pathways, primarily involving the oxidation of ethanol and subsequent chemical reactions. Vaporization and Mixing, Ignition and Combustion & Ethanol Combustion processes remain the same.

Acetone Formation:

Acetone forms from acetaldehyde and other combustion intermediates through various pathways, including:

Condensation:

Acetaldehyde (formed from ethanol combustion) reacts further through condensation reactions with other reactive intermediates, such as methyl radicals (CH₃), to form acetone.

Oxidation:

Acetaldehyde and other intermediates undergo further oxidation reactions, leading to the formation of acetone. For example, acetaldehyde reacts with hydroxyl radicals (OH) or molecular oxygen (O₂) to produce acetone.

$$\begin{gathered}

\mathrm{C}_2 \mathrm{H}_5 \mathrm{OH}+3 \mathrm{O}_2 \rightarrow 2 \mathrm{CH}_3 \mathrm{CHO}+3 \mathrm{H}_2 \mathrm{O} \\

2 \mathrm{CH}_3 \mathrm{CHO} \rightarrow \mathrm{CH}_3 \mathrm{COCH}_3+\mathrm{CH}_3 \mathrm{CHOHCHO}

\end{gathered}$$

This reaction involves the condensation of two molecules of acetaldehyde to form acetone (CH₃COCH₃) and an intermediate compound, acetal (CH₃CHOHCHO).

D. Mitigation Strategies for Un-Regulated Emissions

Reducing the emissions of formaldehyde, acetaldehyde, and acetone from diesel-ethanol engines is a complex process that requires a comprehensive approach. This approach involves addressing combustion efficiency, fuel composition, and emission control technologies. Some of the mitigation strategies that can be used to reduce these pollutants are presented below:

Optimize Engine Design and Operation:

(1) Improve combustion efficiency by optimizing engine parameters such as injection timing, compression ratio, and air-fuel ratio.

(2) Use advanced combustion technologies like homogeneous charge compression ignition (HCCI), stratified charge combustion, or low-temperature combustion (LTC) to minimize incomplete combustion.

(3) Implement exhaust gas recirculation (EGR) to reduce combustion temperatures and decrease the formation of aldehydes.

Fuel Formulation:

(1) Optimize the blend ratio of diesel and ethanol to achieve better combustion characteristics and reduce emissions of aldehydes.

(2) Use higher-quality ethanol with lower impurities to minimize the formation of aldehydes and ketones.

(3) Incorporate additives into the fuel formulation that promote more complete combustion and reduce the formation of aldehydes and ketones.

Exhaust Gas Aftertreatment:

(1) Install diesel oxidation catalysts (DOCs) or selective catalytic reduction (SCR) systems to convert aldehydes and ketones into less harmful compounds.

(2) Utilize particulate filters to trap particulate matter and organic compounds, including aldehydes and ketones, from the exhaust stream.

Advanced Engine Control and Calibration:

(1) Implement advanced engine control strategies and calibration techniques to optimize fuel injection parameters and exhaust gas recirculation rates for minimizing aldehyde and ketone formation.

(2) Utilize dynamic control algorithms to adjust engine operation in real-time based on operating conditions and emission requirements.

The emissions of formaldehyde, acetaldehyde, and acetone from diesel-ethanol engines can be reduced effectively by implementing the above-mentioned mitigation strategies.

These strategies will help improve air quality, environmental sustainability and human health due to inhaled air. Future research and development efforts in engine technology and fuel formulation will continue to drive advancements in un-regulated emission reduction strategies for diesel-ethanol engines

E. Limitations of the Method Used for the Collection of Samples and Analysis of Un-Regulated Emissions

i. Reactivity with Other Compounds:

Nitrogen dioxide (NO₂) and carbon monoxide (CO) in the sampled air can react with DNPH solution, consuming the DNPH and possibly underreporting carbonyl contents, especially formaldehyde and acetaldehyde. However, to overcome this, in our study, the collected sample was stored below 4℃ to avoid any secondary reaction with other pollutants present in the exhaust gas. Additionally, a DNPH cartridge was used in place of a DNPH solution, which reduces the problem of underreporting of carbonyl contents and evaporation.

ii. Sampling Conditions:

The effectiveness of the DNPH method can be influenced by environmental conditions such as temperature and humidity. High humidity levels can lead to hydrolysis of the derivatives, affecting the accuracy of the measurements. As explained earlier, in our study, the collected sample was stored below 4℃ till the completion of the analysis using HPLC.

iii. Storage Stability:

Samples collected using DNPH cartridges have stability issues over time. If not analyzed promptly, the derivatives can degrade, leading to inaccurate quantification of the original compounds. In our study, the analysis was completed within 24 hours of the test to overcome above mentioned issues.

iv. Sampling Time Variation

Since the measurement of unregulated emissions lacks a defined protocol. The concentration and final outcomes may be impacted by changes in the sample period and flow rate. Therefore, a standard technique needs to be developed in order to acquire repeated outcomes.

F. Environmental and Health Implications

The environmental and health implications of each un-regulated pollutant are shown in Table 7. With the use of diesel-ethanol (D20) blended fuel some of the carbonyl pollutants increased while others decreased as compared to base diesel.

Table 7. Environmental and health implications

G. Comparison of Results with Existing Literature:

In this sub-section, the results discussed in earlier sections are compared with other similar contemporary studies available in the literature. Primarily, the current study reports that formaldehyde and acetaldehyde emissions increased by 115% and 3293%, respectively, whereas acetone emissions were reduced by 89% for D20 fuel over base diesel (D0) in a three-cylinder diesel engine used for non-road application, tested over 8 mode mass emission test cycle as per ISO 8178-C1 standard. The engine was operating in the range of 1300-2150 rpm.

In the first comparison, Song et al. [18] investigated carbonyl compound emissions in a six-cylinder heavy-duty diesel engine fueled with diesel and diesel-ethanol blend (15% by volume ethanol). The engine was tested over 13 mode test cycles as per ECE R-49 test standard. The authors reported an increase in formaldehyde, acetaldehyde, and acetone emissions by 451%, 143%, and 241%, respectively, at the 1200 – 2600 rpm range. Although the engine type, test cycle, and ethanol blending percentage in the present study are different from those employed by Song et al., a significant increase in formaldehyde and acetaldehyde emissions is evident in both studies. The acetone emissions have been reported to increase by Song et al., whereas they have decreased due to ethanol blending in the present study.

In the second comparison, Li et al. [19] investigated regulated and unregulated emissions in a four-cylinder direct injection diesel engine fueled with diesel and diesel-ethanol blend (15% by volume ethanol). The engine was tested for different IMEP ranging from 3-9 bar. The authors reported an increase in formaldehyde and acetaldehyde emissions by 200% and 300%, respectively, at 1500 rpm. Although the engine type, test procedure, and ethanol blending percentage in the present study are different from those employed by the study [19], a significant increase in formaldehyde and acetaldehyde emissions is evident in both studies. The acetone emissions have not been reported by the study [19] for comparison with the present study.

In the third comparison, Yan et al. [20] investigated both regulated and unregulated emissions in a single-cylinder diesel engine without any modifications. The engine was fueled with a diesel and a diesel-ethanol blend of 20% (E20). The engine was tested at constant speed and constant torque outputs. At a rated RPM of 1500, the formaldehyde and acetaldehyde emissions of E20 increased by 4.2% and 200%, respectively, at the rated load compared to diesel. However, acetone emissions were not measured in this study. Although the engine type, test cycle, and ethanol blending percentage in the present study are different from those employed by Yan et al., an increase in formaldehyde and acetaldehyde emissions is evident in both studies.

In the fourth comparison, He et al. [11] investigated the unregulated emissions of ethanol-diesel blend percentage of up to 30% (E30) by volume. The blends were tested on a twin cylinder naturally aspirated direct injection diesel engine at constant speed for various load conditions. The authors reported that at rated RPM and rated power output, the formaldehyde emissions of E30 increased by about 2-3% compared to that of diesel but showed a negligible increase when compared to E10. However, the Acetaldehyde emissions increased by almost 150% and 66% for E30 and E10, respectively, as compared to that of diesel emissions. This study also concluded that there is a rise in aldehyde and formaldehyde emissions when ethanol is added to diesel, supporting the findings of the present study.

In the fifth comparison, Haupt et al. [21] investigated the effects of Ethanol fuel on a 9L HD Euro III diesel engine equipped with an aftercooler and a turbocharger. The engine was tested in the European Stationery Cycle (ESC) stationery cycle. The authors reported that the system produced about 1600% and 9800% more formaldehyde and acetaldehyde emissions, respectively, as compared to the baseline diesel engine. This study concluded that there is a rise in aldehyde and formaldehyde emissions when ethanol is used as a fuel, indirectly supporting the findings of the present study.

H. ANOVA of Un-Regulated Emissions in Terms of Fuel Properties

In the present study, a two-way ANOVA test was conducted to examine the statistical significance of the measured un-regulated emissions (formaldehyde, acetaldehyde, acetone, and, acrolein) in terms of critical fuel properties of blended diesel (Gross Calorific Value, Cetane Number, and Flash Point) that witnessed a significant deviation from the corresponding base diesel fuel properties.

(1) Effect on Formaldehyde

Table 8 shows the ANOVA results for formaldehyde emissions. From the analysis, it can be seen that the value of P for cetane number and Gross CV is less than 0.05. Hence, these properties have statistically significant effects on formaldehyde emissions. The higher the F value, the more is the significance. The F value of Gross CV is higher than the Cetane Number, which means that Gross CV is the most significant factor for the formation of formaldehyde due to ethanol blended diesel fuel.

Table 8. ANOVA output for formaldehyde

(2) Effect on Acetaldehyde

Table 9 shows the ANOVA results for acetaldehyde emissions. From the analysis, it can be seen that the value of P for Gross CV is less than 0.05, which means that Gross CV is the only statistically significant factor for the formation of acetaldehyde due to ethanol blended diesel fuel.

Table 9. ANOVA output for acetaldehyde

(3) Effect on Acetone

Table 10 shows the ANOVA results for acetone emissions.

From the analysis, it can be seen that the value of P for all three properties (Gross CV, Cetane Number, and Flash Point) is less than 0.05, which means all three properties are statistically significant factors for the formation of acetone. However, based on higher F value, Gross CV is the most significant impact on the formation of acetone due to ethanol blended diesel fuel.

Table 10. ANOVA output for acetone

(4) Effect on Acrolein

Table 11 shows the ANOVA results for acrolein emissions. From the analysis, it can be seen that the value of P for all three properties (Gross CV, Cetane Number, and Flash Point) is less than 0.05, which means all three properties are statistically significant factors for the formation of acrolein. However, based on higher F value, Gross CV is the most significant impact on the formation of acrolein due to ethanol blended diesel fuel.

Table 11. ANOVA output for Acrolein