Sensitivity of Diesel Particulate Material Emissions and Composition to Blends of Petroleum Diesel and Biodiesel Fuel

A number of investigations have examined the impact of the use of biodiesel on the emissions of carbon dioxide and regulated emissions, but limited information exists on the chemical composition of particulate matter from diesel engines burning biodiesel blends. This study examines the composition of diesel particulate matter (DPM) emissions from a commercial agriculture tractor burning a range of biodiesel blends operating under a load that is controlled by a power take off (PTO) dynamometer. Ultra-low sulfur diesel (ULSD) fuel was blended with soybean and beef tallow based biodiesel to examine fuels containing 0% (B0), 25% (B25), 50% (B50), 75% (B75), and 100% (B100) biodiesel. Samples were then collected using a dilution source sampler to simulate atmospheric dilution. Diluted and aged exhaust was analyzed for particle mass and size distribution, PM_2.5 particle mass, PM_2.5 organic and elemental carbon, and speciated organic compounds. PM_2.5 mass emissions rates for the B25, B50, and B75 soybean oil biodiesel mixtures had 20%–30% lower emissions than the petroleum diesel, but B100 emissions were about 40% higher than the petroleum diesel. The trends in mass emission rates with the increasing biodiesel content can be explained by a significant decrease in elemental carbon (EC) emissions across all blending ranges and increasing organic carbon (OC) emissions with pure biodiesel. Beef tallow biodiesel blends showed similar trends. Nevertheless, it is important to note that the study measurements are based on low dilution rates and the OC emissions changes may be affected by ambient temperature and different dilution conditions spanning micro-environments and atmospheric conditions. The results show that the use of biodiesel fuel for economic or climate change mitigation purposes can lead to reductions in PM emissions and a co-benefit of EC emission reductions. Detailed speciation of the OC emissions were also examined and are presented to understand the sensitivity of OC emissions with respect to biodiesel fuel blends.

Copyright 2012 American Association for Aerosol Research     

Influence of fuel sulfur on the characterization of PM10 from a diesel engine

To study the effects of fuel sulfur content on the characteristics of diesel particle emitted from a typical engine used in China, two types of diesel fuel with sulfur content of 30 ppm and 500 ppm were used in this engine dynamometer test under six operation conditions corresponding to 20%, 50% and 80% load at 1400 rpm and 2300 rpm engine speeds, respectively. Gaseous pollutants and particulate matter (PM) emissions were sampled with AVL AMA4000 and Model 130 High-Flow Impactor (MSP Corp), respectively. More specifically, the PM mass, total carbon (TC), organic carbon (OC), elemental carbon (EC) and water-soluble ion distribution were also measured. Compared with high sulfur diesel, the application of low sulfur diesel can lower fuel-based PM emissions by 9.2-56.6%. At 1400 rpm, the low sulfur diesel decreased both OC and EC by 5-34% and about 20%; while at 2300 rpm, the low sulfur fuel decreased OC by 33-57% and increased EC emission, resulting in a lower OC/EC ratio. The evidence implicating that OC oxidation was promoted by low sulfur diesel, but the effect on EC oxidation was dependent on engine speed. The linear regression has been conducted between TC and PM₁₀, and the slopes were 0.88 and 0.80 for low sulfur diesel and high sulfur one, respectively. Higher sulfate content was detected in the 0.13 μm particles when using the high sulfur diesel, but the percentage of sulfate was 0.9% for PM₁₀ from both diesel fuels. Comparing with that of 500 ppm, EC increased sharply to a maximum of 114% in particles of 0.13 μm when using 30 ppm sulfur diesel at 2300 rpm.     

Attempts to reduce NOx exhaust emissions by using reformulated biodiesel

Biodiesel is a renewable, domestically produced fuel that has been shown to reduce particulate, hydrocarbon, and carbon monoxide emissions from diesel engines. Under some conditions, however, biodiesel produced from certain feedstocks has been shown to cause an increase in nitrogen oxides (NO_x). This is of special concern in urban areas that are subject to strict environmental regulations. Although soy-based biodiesel may increase the emission of nitrogen oxides, it is the most easily accessible in North America. We investigated two routes to reformulate soy-based biodiesel in an effort to reduce nitrogen oxide emissions. In one of these, soy-oil methyl esters were modified by conversion of a proportion of the cis bonds in the fatty acid chains of its methyl esters to their trans isomers. In the other approach, polyol derivatives of soybean oil were transesterified to form soy methyl polyol fatty acid esters. The NO_x emissions of these modified biodiesels were then examined, using a Yanmar L100 single cylinder, four stroke, naturally aspirated, air cooled, direct injection diesel engine. Using either isomerized methyl oleate or isomerized soy biodiesel, at 20% blend level in petroleum diesel (‘B20’), nitrogen oxide emissions were elevated by between 1.5 and 3 percentage points relative to the combustion of a B20 blend of commercial biodiesel. Nitrogen oxide emissions were reduced in proportion to blend level during the combustion of polyol biodiesel, with a 20% blend in petrodiesel resulting in a reduction of about 4.5 percentage points relative to the emissions of a comparable blend of commercial soy biodiesel.     

Biodiesel from safflower oil and its application in a diesel engine

Safflower seed oil was chemically treated by the transesterification reaction in methyl alcohol environment with sodium hydroxide (NaOH) to produce biodiesel. The produced biodiesel was blended with diesel fuel by 5% (B5), 20% (B20) and 50% (B50) volumetrically. Some of important physical and chemical fuel properties of blend fuels, pure biodiesel and diesel fuel were determined. Performance and emission tests were carried out on a single cylinder diesel engine to compare biodiesel blends with petroleum diesel fuel. Average performance reductions were found as 2.2%, 6.3% and 11.2% for B5, B20 and B50 fuels, respectively, in comparison to diesel fuel. These reductions are low and can be compensated by a slight increase in brake specific fuel consumption (Bsfc). For blends, Bsfcs were increased by 2.8%, 3.9% and 7.8% as average for B5, B20 and B50, respectively. Considerable reductions were recorded in PM and smoke emissions with the use of biodiesel. CO emissions also decreased for biodiesel blends while NO_x and HC emissions increased. But the increases in HC emissions can be neglected as they have very low amounts for all test fuels. It can be concluded that the use of safflower oil biodiesel has beneficial effects both in terms of emission reductions and alternative petroleum diesel fuel.     

Performance and combustion characteristics of a DI diesel engine fueled with waste palm oil and canola oil methyl esters

This study discusses the performance and combustion characteristics of a direct injection (DI) diesel engine fueled with biodiesels such as waste (frying) palm oil methyl ester (WPOME) and canola oil methyl ester (COME). In order to determine the performance and combustion characteristics, the experiments were conducted at the constant engine speed mode (1500 rpm) under the full load condition of the engine. The results indicated that when the test engine was fueled with WPOME or COME, the engine performance slightly weakened; the combustion characteristics slightly changed when compared to petroleum based diesel fuel (PBDF). The biodiesels caused reductions in carbon monoxide (CO), unburned hydrocarbon (HC) emissions and smoke opacity, but they caused to increases in nitrogen oxides (NO_x) emissions.     

Fuel consumption and emissions from a diesel power generator fuelled with castor oil and soybean biodiesel

This work investigates the impacts on fuel consumption and exhaust emissions of a diesel power generator operating with biodiesel. Fuel blends with 5%, 20%, 35%, 50%, and 85% of soybean biodiesel in diesel oil, and fuel blends containing 5%, 20%, and 35% of castor oil biodiesel in diesel oil were tested, varying engine load from 9.6 to 35.7 kW. Specific fuel consumption (SFC) and the exhaust concentrations of carbon dioxide (CO₂), carbon monoxide (CO), and hydrocarbons (HC) were evaluated. The engine was kept with its original settings for diesel oil operation. The results showed increased fuel consumption with higher biodiesel concentration in the fuel. Soybean biodiesel blends showed lower fuel consumption than castor biodiesel blends at a given concentration. At low and moderate loads, CO emission was increased by nearly 40% and over 80% when fuel blends containing 35% of castor oil biodiesel or soybean biodiesel were used, respectively, in comparison with diesel oil. With the load power of 9.6 kW, the use of fuel blends containing 20% of castor oil biodiesel or soybean biodiesel increased HC emissions by 16% and 18%, respectively, in comparison with diesel oil. Exhaust CO₂ concentration did not change significantly, showing differences lower than ±3% of the values recorded for diesel oil operation, irrespective of biodiesel type, concentration and the load applied. The results demonstrate that optimization of fuel injection system is required for proper engine operation with biodiesel.     

Determination of performance and exhaust emissions properties of B75 in a CI engine application

In this study, performance and exhaust emissions of biodiesel in a compression ignition engine was experimentally investigated. Therefore, biodiesel has been made by transesterification from cotton seed oil and then it was mixed with diesel fuel by 25% volumetrically, called here as B75 fuel. B75 fuel was tested, as alternative fuel, in a single cylinder, four strokes, and air-cooled diesel engine. The effect of B75 and diesel fuels on the engine power, engine torque and break specific fuel consumption were clarified by the performance tests. The influences of B75 fuel on CO, HC, NOx, Smoke opacity, CO₂, and O₂ emissions were investigated by emission tests. The engine torque and power, for B75 fuel, were lower than that of diesel fuel in range of 2-3%. However, for the B75, specific fuel consumption was higher than that of diesel fuel by approximately 3%. CO₂, CO, HC, smoke opacity and NO_x emissions of B75 fuel were lower than that of diesel fuel. The experimental results showed that B75 fuel can be substituted for the diesel fuel without any modifications in diesel engines.     

Comparative study of performance and emissions of a diesel engine using Chinese pistache and jatropha biodiesel

An experimental study of the performances and emissions of a diesel engine is carried out using two different biodiesels derived from Chinese pistache oil and jatropha oil compared with pure diesel. The results show that the diesel engine works well and the power outputs are stable running with the two selected biodiesels at different loads and speeds. The brake thermal efficiencies of the engine run by the biodiesels are comparable to that run by pure diesel, with some increases of fuel consumptions. It is found that the emissions are reduced to some extent when using the biodiesels. Carbon monoxide (CO) emissions are reduced when the engine run at engine high loads, so are the hydrocarbon (HC) emissions. Nitrogen oxides (NOx) emissions are also reduced at different engine loads. Smoke emissions from the engine fuelled by the biodiesels are lowered significantly than that fuelled by diesel. It is also found that the engine performance and emissions run by Chinese pistache are very similar to that run by jatropha biodiesel.     

Performance and emission study of waste anchovy fish biodiesel in a diesel engine

Waste anchovy fish oils transesterification was studied with the purpose of achieving the conditions for biodiesel usage in a single cylinder, direct injection compression ignition. With this purpose, the pure biodiesel produced from anchovy fish oil, biodiesel-diesel fuel blends of 25%:75% biodiesel-diesel (B25), 50%:50% biodiesel-diesel (B50), 75%:25% biodiesel-diesel (B75) and petroleum diesel fuels were used in the engine to specify how the engine performance and exhaust emission parameters changed. The fuel properties of test fuels were analyzed. Tests were performed at full load engine operation with variable speeds of 1000, 1500, 2000 and 2500 rpm engine speeds. As results of investigations on comparison of fuels with each other, there has been a decrease with 4.14% in fish oil methyl ester (FOME) and its blends' engine torque, averagely 5.16% reduction in engine power, while 4.96% increase in specific fuel consumption have been observed. On one hand there has been average reduction as 4.576%, 21.3%, 33.42% in CO₂, CO, HC, respectively; on the other hand, there has been increase as 9.63%, 29.37% and 7.54% in O₂, NO_x and exhaust gas temperature has been observed. It was also found that biodiesel from anchovy fish oil contains 37.93 wt.% saturated fatty acids which helps to improve cetane number and lower NO_x emissions. Besides, for biodiesel and its blends, average smoke opacity was reduces about 16% in comparison to D2. It can be concluded that waste anchovy fish obtained from biodiesel can be used as a substitute for petroleum diesel in diesel engines.     

Performance of compression ignition engine with mahua (Madhuca indica) biodiesel

The performance of biodiesel obtained from mahua oil and its blend with high speed diesel in a Ricardo E6 engine has been presented in this paper together with some of its fuel properties. These properties were found to be comparable to diesel and confirming to both the American and European standards. Engine performance (brake specific fuel consumption, brake thermal efficiency and exhaust gas temperature) and emissions (CO, smoke density and NO_x) were measured to evaluate and compute the behaviour of the diesel engine running on biodiesel. The reductions in exhaust emissions and brake specific fuel consumption together with increase brake power, brake thermal efficiency made the blend of biodiesel (B20) a suitable alternative fuel for diesel and thus could help in controlling air pollution.     

Physical-chemical properties of waste cooking oil biodiesel and castor oil biodiesel blends

This work presents the physical-chemical properties of fuel blends of waste cooking oil biodiesel or castor oil biodiesel with diesel oil. The properties evaluated were fuel density, kinematic viscosity, cetane index, distillation temperatures, and sulfur content, measured according to standard test methods. The results were analyzed based on present specifications for biodiesel fuel in Brazil, Europe, and USA. Fuel density and viscosity were increased with increasing biodiesel concentration, while fuel sulfur content was reduced. Cetane index is decreased with high biodiesel content in diesel oil. The biodiesel blends distillation temperatures T₁₀ and T₅₀ are higher than those of diesel oil, while the distillation temperature T₉₀ is lower. A brief discussion on the possible effects of fuel property variation with biodiesel concentration on engine performance and exhaust emissions is presented. The maximum biodiesel concentration in diesel oil that meets the required characteristics for internal combustion engine application is evaluated, based on the results obtained.     

Mitigation of NOx emissions from a jatropha biodiesel fuelled DI diesel engine using antioxidant additives

Biodiesel offers cleaner combustion over conventional diesel fuel including reduced particulate matter, carbon monoxide and unburned hydrocarbon emissions. However, several studies point to slight increase in NO_x emissions (about 10%) for biodiesel fuel compared with conventional diesel fuel. Use of antioxidant additives is one of the most cost-effective ways to mitigate the formation of prompt NO_x. In this study, the effect of antioxidant additives on NO_x emissions in a jatropha methyl ester fuelled direct injection diesel engine have been investigated experimentally and compared. A survey of literature regarding the causes of biodiesel NO_x effect and control strategies is presented. The antioxidant additives L-ascorbic acid, α tocopherol acetate, butylated hydroxytoluene, p-phenylenediamine and ethylenediamine were tested on computerised Kirloskar-make 4 stroke water cooled single cylinder diesel engine of 4.4 kW rated power. Results showed that antioxidants considered in the present study are effective in controlling the NO_x emissions of biodiesel fuelled diesel engines. A 0.025%-m concentration of p-phenylenediamine additive was optimal as NO_x levels were substantially reduced in the whole load range in comparison with neat biodiesel. However, hydrocarbon and CO emissions were found to have increased by the addition of antioxidants.     

Exhaust emissions and health effects of particulate matter from agricultural tractors operating on rapeseed oil methyl ester

Exhaust emissions and their effects on the environment and human health, such as mutagenicity of particulate matter (PM) and ozone-forming potential, must be considered when using an alternative fuel. In the present work, a test engine and two agricultural tractors ran on rapeseed oil methyl ester (biodiesel) or conventional diesel fuel as well as blends thereof. The objective was to detect any disproportionately positive or negative effects depending on blend levels, because conventional diesel fuel and biodiesel can be blended in every ratio. Generally, emissions of regulated compounds changed linearly with the blend level. The known positive and negative effects of biodiesel varied accordingly. Overall, no optimal blend was found. Increasing biodiesel content of the fuel caused a linear increase in benzene emissions in the agricultural five-mode engine test, an effect that may be explained from previous studies on precombustion chemistry. In using the test engine, it was found that PM from biodiesel significantly reduced mutagenic potential compared with that from diesel fuel, although in this work PM masses were found to be reproducibly higher for biodiesel from rapeseed oil compared with conventional diesel fuel. Ozone precursors increased 10–30% when using biodiesel compared with conventional diesel fuel. Emissions of aldehydes and alkenes are mainly responsible for this effect. N₂O emissions increased when using a catalytic converter.     

Fuel properties and nitrogen oxide emission levels of biodiesel produced from animal fats

FAME of lard, beef tallow, and chicken fat were prepared by base-catalyzed transesterification for use as biodiesel fuels. Selected fuel properties of the neat fat-derived methyl esters (B100) were determined and found to meet ASTM specifications. The cold-flow properties, lubricity, and oxidative stability of the B100 fat-derived fuels also were measured. In general, the cold-flow properties of the fat-based fuels were less desirable than those of soy-based biodiesel, but the lubricity and oxidative stability of the fat-based biodiesels were comparable to or better than soy-based biodiesel. Nitrogen oxide (NO_x) emission tests also were conducted with the animal fat-derived esters and compared with soybean oil biodiesel as 20 vol% blends (B20) in petroleum diesel. The data indicated that the three animal fat-based B20 fuels had lower NO_x emission levels (3.2–6.2%) than did the soy-based B20 fuel.     

Analytical study for atomization of biodiesels and their blends in a typical injector: Surface tension and viscosity effects

This study presents analytical comparisons of atomization characteristics of 7 biodiesels and 17 binary and ternary blends with D1 and D2 at 80 °C, using a direct injection injector. The atomization of a genetically modified vegetable oil – Captex 355 – and its corresponding biodiesel were also studied. Results from statistical analysis showed that B100 coconut biodiesel had similar atomization characteristics to D2, because of its similar properties, i.e. density, surface tension and viscosity. No significant difference in drop size was observed for all B5 blends, and B20 blends and B100 biodiesels of palm, soybean, cottonseed, peanut and canola. It implies these stocks of biodiesels and their blends can be used in a DI engine with similar atomization characteristics. Ternary biodiesel blends, with ⩽10 wt.% petroleum diesel, can yield equal drop sizes as some binary blends with large quantities of D1 and D2. The ternary biodiesel blends are likely to reduce pollution from exhaust emissions better than the biodiesel blends with D1 or D2. Captex 355 biodiesel had the best atomization characteristics of all the fuels studied. The Sauter mean diameter (SMD) produced by this fuel was up to 13% and 25% smaller than that of D1 and D2, respectively. The Captex 355 biodiesel may be used as a base in binary or ternary biodiesel blends to achieve better atomization than D1 and D2 in diesel engines.     

Engine performance and emission characteristics of marine fish-oil biodiesel produced from the discarded parts of marine fish

Biodiesel is recognized as a clean alternative fuel or as a fuel additive to reduce pollutant emissions from combustion equipment. Because cultivated land is too limited to grow seed-oil plants sufficient to produce both food and biodiesel, non-land-based oleaginous materials have been considered important sources for the production of the latter. In this study, the discarded parts of mixed marine fish species were used as the raw material to produce biodiesel. Marine fish oil was extracted from the discarded parts of mixed marine fish and refined through a series of pretreatment processes. The refined marine fish oil was then transesterified with methyl alcohol to produce biodiesel, which was used thereafter as engine fuel to investigate its engine performance and emission characteristics. The experimental results show that, compared with commercial biodiesel from waste cooking oil, marine fish-oil biodiesel has a larger gross heating value, elemental carbon and hydrogen content, cetane index, exhaust gas temperature, brake fuel conversion efficiency, NO_x and O₂ emissions, and black smoke opacity and a lower elemental oxygen content, fuel consumption rate, brake-specific fuel consumption rate, equivalence ratio, and CO emission. Compared with ASTM No. 2D diesel, both marine fish-oil and waste cooking-oil biodiesels appear to have a lower gross heating value, cetane index, exhaust gas temperature, equivalence ratio, black smoke opacity, elemental carbon content, and CO emission and a higher fuel consumption rate and elemental oxygen content.     

Exhaust Emissions from an Engine Fueled with Biodiesel from High-Oleic Soybeans

Biodiesel is a fuel comprising mono-alkyl esters of medium to long-chain fatty acids derived from vegetable oils or animal fats. Typically, engines operated on soybean-based biodiesel exhibit higher emissions of oxides of nitrogen (NOx) compared with petroleum diesel. The increase in NOx emissions might be an inherent characteristic of soybean oil’s polyunsaturation, because the level of saturation is known to affect the biodiesel’s cetane number, which can affect NOx. A feedstock that is mostly monounsaturated (i.e. oleate) helps to balance the tradeoff between cold flow and oxidative stability. Genetic modification has produced a soybean event, designated 335-13, with a fatty acid profile high in oleic acid (>85%) and with reduced palmitic acid (<4%). This high-oleic soybean oil was converted to biodiesel and run in a John Deere 4045T 4.5-L four-stroke, four-cylinder, turbocharged direct-injection diesel engine. The exhaust emissions were compared with those from conventional soybean oil biodiesel and commercial No. 2 diesel fuel. There was a significant reduction in NOx emissions (α = 0.05) using the high-oleic soybean biodiesel compared with regular soybean oil biodiesel. No significant differences were found between the regular and high-oleic biodiesel for unburned hydrocarbon and smoke emissions.     

Diesel engine performance and emission characteristics of biodiesel produced by the peroxidation process

Biodiesel is an alternative fuel that is cleaner than petrodiesel. Biodiesel can be used directly as fuel for a diesel engine without having to modify the engine system. It has the major advantages of having high biodegradability, excellent lubricity and no sulfur content. In this study, the biodiesel produced by a transesterification technique was further reacted by using a peroxidation process. Four types of diesel fuel, biodiesel with and without an additional peroxidation process, a commercial biodiesel and ASTM No. 2D diesel were compared for their fuel properties, engine performance and emission characteristics. The experimental results show that the fuel consumption rate, brake thermal efficiency, equivalence ratio, and exhaust gas temperature increased while the bsfc, emission indices of CO₂, CO and NO_x decreased with an increase of engine speed. The three biodiesels showed a higher fuel consumption rate, bsfc, and brake thermal efficiency, while at the same time exhibited lower emission indices of CO and CO₂ as well as a lower exhaust gas temperature when compared to ASTM No. 2D diesel. Moreover, the biodiesel produced with the additional peroxidation process was found to have an oxygen content, weight proportion of saturated carbon bonds, fuel consumption rate, and bsfc that were higher than the biodiesel produced without the additional process; while at the same time the brake thermal efficiency, equivalence ratio, and emission indices of CO₂, CO and NO_x were found to be lower. In particular, biodiesel produced with the addition of the peroxidation process had the lowest equivalence ratio and emission indices of CO₂, CO and NO_x among all of the four test fuels. Therefore, the peroxidation process can be used to effectively improve the fuel properties and reduce emissions when biodiesel is used.     

Comparison of emissions of a direct injection diesel engine operating on biodiesel with emulsified and fumigated methanol

Biodiesel is an alternative fuel for internal combustion engines. It can reduce carbon monoxide (CO), hydrocarbon (HC) and particulate matter (PM) emissions, compared with diesel fuel, but there is also an increase in nitrogen oxides (NO_x) emission. This study is aimed to compare the effect of applying a biodiesel with either 10% blended methanol or 10% fumigation methanol. The biodiesel used in this study was converted from waste cooking oil. Experiments were performed on a 4-cylinder naturally aspirated direct injection diesel engine operating at a constant speed of 1800 rev/min with five different engine loads. The results indicate a reduction of CO₂, NO_x, and particulate mass emissions and a reduction in mean particle diameter, in both cases, compared with diesel fuel. It is of interest to compare the two modes of fueling with methanol in combination with biodiesel. For the blended mode, there is a slightly higher brake thermal efficiency at low engine load while the fumigation mode gives slightly higher brake thermal efficiency at medium and high engine loads. In the fumigation mode, an extra fuel injection control system is required, and there is also an increase in CO, HC and NO₂ (nitrogen dioxide) and particulate emissions in the engine exhaust, which are disadvantages compared with the blended mode.     

Biodiesel engine performance and emissions in low temperature combustion

Engine performance and emission comparisons were made between the use of soy, Canola and yellow grease derived B100 biodiesel fuels and an ultra-low sulphur diesel fuel in the high load engine operating conditions. Compared to the diesel fuel engine-out emissions of nitrogen oxides (NO_x), a high-cetane number (CN) biodiesel fuel produced comparable NO_x while the biodiesel with a CN similar to the diesel fuel produced relatively higher NO_x at a fixed start of injection. The soot, carbon monoxide and un-burnt hydrocarbon emissions were generally lower for the biodiesel-fuelled engine. Exhaust gas recirculation (EGR) was then extensively applied to initiate low temperature combustion (LTC) mode at medium and low load conditions. An intake throttling valve was implemented to increase the differential pressure between the intake and exhaust in order to increase and enhance the EGR. Simultaneous reduction of NO_x and soot was achieved when the ignition delay was prolonged by more than 50% from the case with 0% EGR at low load conditions. Furthermore, a preliminary ignition delay correlation under the influence of EGR at steady-state conditions was developed. The correlation considered the fuel CN and oxygen concentrations in the intake air and fuel. The research intends to achieve simultaneous reductions of NO_x and soot emissions in modern production diesel engines when biodiesel is applied.