THE POSSIBILITY OF INCREASING THE QUANTITY OF OXYGENATES IN FUEL BLENDS WITH NO DIESEL ENGINE MODIFICATIONS

Two fuel kinds of organic origin including rapeseed methyl ester (RME) and ethanol (E) were selected for their di"erent physical-chemical parameters to study the maximum apt volume of oxygenates to mix fossil diesel (D) and establish expectancy to apply D–RME–E blend as a fuel for the unmodi#ed high–speed diesel engine (a combustion chamber consists of a dished piston). $e objective of the article is to provide an explicit relationship between the nature of fuel composition and diesel engine operating parameters. $e results of the carried out tests on the engine oriented on dynamic and emission characteristics using various portions of the before mentioned bio-components in diesel fuel are presented. Engine behaviour seemed to be improved in the presence of ethanol additives in D–RME blend with a reduction in pollutant emissions in exhaust gases, fuel consumption, ameliorated cetane number, ignition delay time and physical-chemical characteristics of the investigated compounds. $e positive and negative aspects of applying bio-based additives in fossil diesel are reported and discussed.


Introduction
e Commission of the European Union initiated a Directive (2003/30/EC) calling for a 5.75% fuel replacement by biofuels (energy base) in 2010. Currently, various standards and speci cations set rather tight limits to the composition and properties of motor fuels. It should be noted that only diesel fuel containing 3-5% of biodiesel can ful l the current fuel speci cation and be sold as general motor fuel.
According to omson et al. (1998) and Van Gerpen (1996), there are several problems of applying RME to be overcome (unstable cetane number depending on storage time and participating glycerol content).
Following long-term storage, signi cant changes in cetane number (CN) are observed, especially in fuels distilled as a re ning step. During the process of distillation, natural antioxidants such as tocopherols are removed, so that the resulting fuels are more susceptible to oxidative degeneration. Whereas the distillation step itself has no impact on cetane number, oxidation leads to a marked increase. us, omson et al. (1998) reported that the cetane number of rapeseed oil methyl and ethyl esters increased by more than 12 a er a storage period of 24 months. It is argued that hydro peroxides formed during the oxidation of fatty acid esters are responsible for this behaviour, which appears probable, as peroxide compounds are actually discussed as cetane improver additives (Van Gerpen 1996). As a consequence, literature values for cetane numbers considerably di er and experts argue that this data is hardly comparable (Mittelbach and Remschmidt 2004).
In addition to the discussed parameters, a variable in another process in uences the use of biodiesel. Basically, the process of producing biodiesel inevitably requires that a er each transesteri cation step, the glycerol layer has to be separated and removed from the reaction mixture. However, various melted content of glycerol regularly participating in rapeseed methyl ester content can be an occasion of the foul-up of the diesel engine. Unburned glycerol residues originating on the upper part of the cylinder nearby the compression collar (see Fig. 1). e growing upscale layer may a ect abrading the moving parts potentially increasing a risk of seizing. e unburned residues also intended to form on the fuel injectors (see Fig. 2). A thick layer covered injector nozzles strongly worsening fuel spray shaping quality directly in uencing the process of combustion. e content of free glycerol in biodiesel depends on the production process and is therefore the major criterion of fuel quality. High volumes may stem from the insu cient washing of the ester product making glycerol separate during storage once methanol as the common solvent has evaporated (Mittelbach and Remschmidt 2004).
Optimizing the combustion process (i.e. reducing NO x and PM emissions without serious compromises in fuel consumption) requires a profound knowledge of all formation processes involved. Biodiesel is an oxygenated fuel, approximately 10 by volume that exhibits cetane characteristics exceeding that of petroleum diesel fuel (Kwanchareon et al. 2007). Some combustion characteristics of mineral diesel and oxygenated biofuel blends are as follows: various proportions (by volume) of a rapeseed methyl ester addition to mineral diesel distinguish an increased cetane number of the blend (see Fig. 3). 5 (by volume) of ethanol used as an additive to B15 blend reduced a combustible cetane number of the mixture that became equal to fossil diesel.
Ethanol solubility in diesel is a ected mainly by two factors covering temperature and water content of the blend. At warm ambient temperatures, dry ethanol blends readily with diesel fuel. However, at about 10 0 C below, the two fuels separate and the above mentioned temperature limit that is easily exceeded in many parts of the world, for a large portion of the year, works against a wider application of diesel fuel-ethanol blends.
Precluding this separation can be accomplished by adding biodiesel that acts as a bridging agent through molecular compatibility and bonding to produce a homogeneous blend (Hansen et al. 2005;Raslavičius and Bazaras 2009).
It was established, that small additional quantities of ethanol to pure RME intended to prolong a transesteri cation step of biodiesel which is to convert all remaining glycerides into the ester product. A similar situation is faced discussing blends of the three-component D-RME-E biodiesel fuel, whereas rapeseed methyl ester serves as a RME-E solvent and bio-component at the same time. e recent amendment to D-RME blends containing more than 20 of biodiesel (v/v) considers the admixtures of 5-7 (v/v) of dehydrated ethyl alcohol (Raslavičius and Bazaras 2009). Using RME in conjunction with ethanol allows in the complex way to increase a quantity of oxygenates to be blended with fossil diesel while no engine modi cations are required to avoid possible power damages to the unit (Raslavičius 2009).

Objects and Methods
Rapeseed methyl ester and dehydrated ethanol were selected to study a possibility of increasing the quantity of oxygenates in D-RME-E blend.  )). e main requirements of the European standard for the investigated types of fuel are presented in Table 1.
For fossil diesel and RME dosage, Simax 1000-ml graduated glass conical ask with stopper was used (ISO 4788:2005, error r5 ml (0.5 ), Class A). Ethanol additives were dosed with the help of Simax 100-ml burette with straight glass one-channel stopcock (ISO 4788:2005, error r0.2 ml (0.2 ), Class B). e components of the tested blend were poured into the 20 l capacity tank made of pressure proof polythene and having a stopcock. Combustible compounds (see Table 2) were prepared by actively shaking the tank for about 5 minutes. A separate tank was used for the each type of fuel.
e experiments were carried out using the diesel engine D144 of 37 kW capacity (see Table 3) installed on the load stand KI 5542 (see Fig. 4). During the stand experiments, energy and emission characteristics of engine operation using multi-component fuel blends were established. e composition of exhaust gases and brake speci c fuel consumption (BSFC) rates were achieved by increasing engine load at the nominal revolution frequency of 1600 min -1 (see Table 4). Depending on the varied parameter, the following characteristics were established: • Blend composition. Independent variable -BSFC; • Engine load. Independent variable -e ective power P.  Accomplishing order for stand tests on the diesel engine: • running at fast idling speed until the engine attains its normal working temperature; • establishing engine speed characteristics; • running the engine for 5-7 min in the established operating mode; • performing measuring tests on fuel consumption and exhaust emission; depending on engine load, testing fuel consumption is accomplished as follows: measuring the time of 100 g fuel burnt out for operating mode 1 as well as the time of 200 g fuel burnt for operating modes 2-5 (see Table 3). Measuring procedures reiteration -5 times; • running the engine for 5-7 min at no load mode; • engine shutdown; • ejecting the investigated type of fuel out of the lters and supply system; • replacing a ne lter element; • ful lling the supply system with the following type of fuel as well as participating air be removed with the help of a manually operating pump; • starting-up the engine; • running the engine at no load mode for 10-15 min. to burn out fuel residues le over at a highpressure pump, pipes and injectors; • repeating straight the above mentioned procedures starting from the establishing the engine's speed characteristics.

Results and Discussion
All test runs were conducted on stand in steady state condition. Measurement points were chosen so that the comparison of the engine parameters and emission could be obtained for the same load but for a di erent proportion of ethanol to B30. Four ratios of bio-additives were respectively added into fossil diesel and used as fuel for the diesel engine. With regard to a huge quantity of the measured values, three basic loads actual for the exploitation of heavy duty transport means were selected to demonstrate the obtained results: low (6 kW), average (18 kW) and high (30 kW).
Ethanol as a compound to increase the economy of biodiesel blends. In general, engine operation on ethanol in the conducted tests on biodiesel blend posed no signi cant drawbacks. e brake speci c fuel consumption (BSFC) of B30 blend before and a er adding ethanol additives is shown in Fig. 5.
As shown in Fig. 5, in all ranges of the engine load, the lowest fuel consumption was obtained using basic fuel (B30) containing 7% (v/v) of ethanol. e brake speci c fuel consumption of B30, B30+5%E and B30+10%E is higher than that of fossil diesel, however, when adding 7% of the total volume of ethanol to the basic fuel, they have the same fuel consumption indicating that combining various oxygenated additives can e ectively improve fuel economy. It should be emphasized that a er sharing 5% (v/v) of the ethanol additive, a positive e ect has been achieved. e above mentioned circumstance can be explained by two factors. First, small quantities of alcohol can act as co-solvents to increase the solubility of glycerol residues in biodiesel which ensures not only better exploitation characteristics of the diesel engine but also improves the combustion process leading to fuel economy. Comparing two di erent types of oxygenated fuel additives to fossil diesel, we must admit that the intersolubility of components in the D-RME-E system was substantially high and show the optimal results. Second, the presence of the small quantities of ethanol, due to its pure in ammation characteristics, can cause improvement in the cetane number of B30 thus becoming comparable to fossil diesel. Only a fair increase in the BSFC of B30+10%E blend has been observed due to a signicant decrease in the heating value and viscosity of fuel. e temperature of exhaust gases slightly decreased at higher alcohol concentrations due to the high evaporative heat of ethanol taking o heat from combustion space.
Exhaust gas emissions for oxygenated fuel blends. e results of the evaluation of the selected engine emission parameters are demonstrated in the graphs depending on the emission parameter of alcohol concentration. All parameters are calculated under standard atmospheric conditions. Particulate emissions from the combustion of fossil diesel contain two major fractions (Molero de Blass 1998): 1. Material arising from the organic content of fuel and its failure to complete the burn-out process: • unburned hydrocarbons (smoke); • particulates formed via gas phase combustion or pyrolisis (soot); • cenospheres produced from cracked fuel or carbon along with ash (coke). 2. Material from the inorganic content of fuel: ash. e results of PM emissions di er widely depending on the tested fuels, cycles, engines and exhaust gas aftertreatment systems used (Mittelbach and Remschmidt 2004). A decrease in carbon soot emissions of the engine fuelled with bio-based diesel blends is explained by the oxygen content of fuel (see Fig. 6).
It enhances oxygen availability within the cylinder during combustion and thus reduces the pyrolisis of the unburned and partly burnt compounds which would lead to the formation of soot. In general, the total PM mass of B30 combustion was lower than that of conventional diesel under all engine operating conditions. e combustion of oxygenated biodiesel (B30) improves engine-out particulate matter emission. Blending diesel fuel with rapeseed methyl ester could unlock potential performance synergies in the fuel properties (e.g. O 2 content in RME and higher cetane number) of such blends and bene t engine performance and emissions. However, a further increase in the biodiesel ratio in diesel fuel becomes unacceptable due to the fact that engine modi cations are required. e use of ethanol to enrich biodiesel blends has, therefore, received considerable attention with particular emphasis on adapting fuel to meet the requirements of the engine. It is mostly used as a fuel additive. e results indicate that the PM emission of the engine operating on 5% and 7% ethanol-B30 blends signi cantly improved when compared to pure diesel. However, in the case of 10% ethanol-B30 blend, a quantity of particulate matter in exhaust gases remained more-or-less in the range of pure B30 with a tendency to increase. e engines fuelled with bio-based combustible mixtures distinguish for their increased emissions of nitrogen oxides (see Fig. 7). e major source of NO x production from nitrogen-bearing fuels such as biodiesel and ethanol is the conversion of fuel bound nitrogen to NO x during combustion. Although the complete mechanism is not fully understood, there is a primary path of formation involving the oxidation of volatile nitrogen species during the initial stages of combustion. During release and prior to the oxidation of volatiles, nitrogen Particulate matter emission, mg/m 3 reacts to form several intermediaries oxidized into NO at a further stage. If the volatiles evolve into a reducing atmosphere, the evolved nitrogen can readily be made to form nitrogen gas rather than NO x . Under test conditions reported herein, we have demonstrated that B30+5 E and B30+7 E blends have lower NO x emissions than pure B30 blend. Additionally, for the tested engine used in this study, small doses of ethanol did not increase NO x emission levels above those measured for fossil diesel which indicated that under conditions set out in our case, D-RME-E biodiesel was NO x neutral. is decrease in NO x is signi cant because it eliminates an increase in NO x emissions observed when a 30% blend of rapeseed methyl ester is substituted for pure diesel. is suggests that by judiciously blending biofuels from di erent feedstock, NO x -neutral biodiesel fuel can be obtained.
Carbon monoxide emission from the diesel engine with di erent blends is shown in Fig. 8. Carbon monoxide gas is a toxic byproduct of all hydrocarbon combustion that is also reduced by increasing the oxygen content of fuel. More complete oxidation of fuel results in more complete combustion of carbon dioxide rather than in leading to the formation of carbon monoxide. CO emission has increased along with an increase in load conditions for diesel and biodiesel blended fuels. Fig. 8 shows di erences in the levels of the emission of carbon monoxide emitted by the tractor power unit between two engine characteristics: at the speed of maximum torque (1600 min -1 ) as well as at low and average loads. ese di erences fall within the range from 30% to 35% and are the least signi cant for B30 fuel having 7% (v/v) of ethanol content. In general, an addition of rapeseed methyl ester (RME) to pure fossil diesel causes a decrease in the emission levels of carbon monoxide dramatically. Must to admit, the emission of carbon monoxide diminishes when operating a highspeed diesel engine under overloaded mode conditions. e ndings of reducing CO and hydrocarbon (HC) emissions of biodiesel fuels are attributed to the oxygen content of rapeseed methyl ester amounting to about 11% which leads to more complete combustion. As oxygenated seed -corn hydrocarbon, biodiesel itself burns cleanly as well as improves the e ciency of combustion in the blends with diesel fuel. In a 30% biodiesel blend, there will be a noticeable change in the odor and smoke of exhaust.
Unburnt hydrocarbons generally stem from the regions in the combustion chamber in which fuel is diluted with air to such a high extent that the mixture fails the process of complete combustion (Mittelbach and Remschmidt 2004). e concentration of unburnt HC emitted from these over-lean regions depends on the amount of fuel injected during the ignition delay period that is shorter for RME due its higher cetane number, and therefore hydrocarbon emissions decrease correspondingly (see Fig. 9).
Not appreciating a type of fuel used for the diesel engine, the fact was under the spotlight that hydrocarbon emission values peaked at low load (6 kW) mode as well as those emitted from the average or high loads were considerably reduced. While using a B30+7 E blend, the emissions of hydrocarbons (HC) were signi cantly reduced compared to test results on baseline diesel fuel. A combustible mixture on the basis of D-RME-E blend provided better fuel spray penetration leading to the e cient combustion process. Increasing a share of dehydrated ethyl alcohol to 10 (v/v) in B30 blend a ects rising up the quantity of hydrocarbon compounds in exhaust gases. is trend was perhaps due to the di erent nature of oxygenates distinguished for severely di erent physical-chemical characteristics laying special emphasis on the su cient and spare amount of ethanol needed to dissolve glycerol residues in biodiesel.
The chemical behaviour of the oxygenated fuel blends. Biodiesel solvent properties cause the degradation of natural rubber hoses and gaskets. Generally, B30 blend and the blends below do not encounter this problem. is is typically only an issue in diesel engine vehicles made before 1993. At that time, fuel lines were commonly made from rubber. Solvent properties in biodiesel disintegrate rubber and sometimes cause leaks in the fuel lines. In these vehicles, biodiesel can still be used but the fuel lines must be monitored for leakage and possibly replaced with vitron fuel lines or other synthetic fuel lines. e current diesel vehicles can run on the proposed D-RME-E biodiesel without any modications.
Due to the solvent properties of biodiesel, the impurities and deposits of para n-based buildup from fossil diesel fuel previously used in the tank may release from edges and ow through the fuel lines to the fuel lter. ese deposits can then plug the fuel lter which is generally problematic only when using pure biodiesel. e fuel lter can be plugged only when using a fuel tank that previously contained fossil diesel fuel. To keep this from happening, it is recommended that the fuel lter be replaced before the engine is converted to biodiesel and a er a few hundred motor-hours of using biodiesel until the fuel system is cleaned of the deposits le from fossil diesel (Raslavičius and Bazaras 2009). To sum up, biodiesel acts as a solvent for cleaning injectors, fuel pump, fuel tank and fuel lines from contaminants fossil diesel leaves.

Conclusions
e above discussion shows that both biodiesel and dehydrated ethyl alcohol can have a considerable in uence on fuel properties such as cetane number with relation to combustion and exhaust emissions. It therefore appears a reasonable concept of enriching certain fatty ester and fossil diesel blends with ethanol having desirable properties in order to amend the exploitation characteristics of the whole fuel. In conclusion, the following points can be taken into account: 1. During stand experiments on the unmodi ed highspeed diesel engine D 144 (a combustion chamber consists of a dished piston), oxygenated blend composition and engine load characteristics were estimated to endeavour to the usefulness of mixing two kinds of bio-based fuels acting together as an improver of combustible compound characteristics and leading to the bigger volumes of conventional diesel to be replaced by biofuels at the same time.
2. Using 5-7% (v/v) of ethanol additives to B30 compound ensures the engine fuel consumption rates close to those of pure mineral diesel thus avoiding BSFC increment biodiesel blends are famous for. 3. Biodiesel fuel admixed with 10% of ethanol (v/v) determines higher BSFC rates and increased exhaust emission of hazardous compounds comparing to the analogically established parameters of B30. 4. To evaluate the pollutant emission of heavy duty transport means for agricultural purpose, a high load (30 kW) engine mode was selected to discuss reasoning that peculiar exploitation characteristic is dominant. Two types of the oxygenated blends (B30 and B30+7%E) were selected to demonstrate an impact of the oxygenated additives (in particular -ethanol) on exhaust emission (fossil diesel emission accepted equal to 100%). Hereby, B30: PM (-23%), NO x (+3%), CO (-16.5%), HC (-28%). And for B30+7%E: PM (-29%), NO x (neutral to D), CO (-21.5%), HC (-35.5%).