Biodiesel production from tall oil with synthesized Mn and Ni based additives: Effects of the additives on fuel consumption and emissions

In this study, biodiesel fuel and fuel additives were produced from crude tall oil that is a by-product in the pulp manufacturing by craft or sulphate pulping process. Fatty acids and resinic acids were obtained from crude tall oil by distillation method. Tall oil methyl ester (biodiesel) was produced from fatty acids. Resinic acids were reacted with NiO and MnO₂ stoichiometrically for production of metallic fuel additives. Each metallic fuel additive was added at the rate of 8 μmol/l and 12 μmol/l to make mixtures of 60% tall oil methyl ester/40% diesel fuel (TE60) for preparing test fuels. Metallic fuel additives improved properties of biodiesel fuels, such as pour point and viscosity values. Biodiesel fuels were tested in an unmodified direct injection diesel engine at full load condition. Specific fuel consumption of biodiesel fuels increased by 6.00%, however, in comparison with TE60, it showed trend of decreasing with adding of additives. Exhaust emission profile of biodiesel fuels improved. CO emissions and smoke opacity decreased up to 64.28% and 30.91% respectively. Low NO_x emission was also observed in general for the biodiesel fuels.     

Potential for reducing emissions in a diesel engine by fuelling with conventional biodiesel and Fischer-Tropsch diesel

A gas-to-liquid (GTL) fuel derived from Low Temperature Fischer-Tropsch process has been tested in an automotive diesel engine fulfilling Euro 4 emissions regulations. Both regulated and non-regulated emissions have been compared with those of a commercial diesel fuel, a commercial biodiesel fuel and a GTL-biodiesel fuel (30% and 70% v/v, respectively) in order to check blending properties, synergistic effects and compatibility between first and second generation production technologies for biofuel consumption in current diesel engines. After presenting a detailed literature review, and confirming that similar efficiencies are attained with the four tested fuels under identical road-like operating conditions (this meaning fuel consumption is inversely proportional to their heating values), significant reductions in smoke opacity, particulate matter emissions and particle number concentration were observed with both GTL and biodiesel fuels, with small changes in NO_x emissions. Compared with the reductions in PM emissions derived from the use of biodiesel fuels, those derived from using GTL fuels were quite similar, despite its lower soot emissions reductions. This can be explained by the lower volatile organic fraction of the PM in the case of GTL. By adequately blending both fuels, a considerable potential to optimise the engine emissions trade-off is foreseen.     

Effects of diesel particulate trap and addition of di-methoxy-methane,di-methoxy-propane to diesel on emission characteristics of a diesel engine

The objective of this investigation was to improve the performance of a diesel engine by adding oxygenated fuel additives of known percentages. The fuel additives di-methoxy-methane (DMM) and di-methoxy-propane (DMP) were separately blended with diesel fuel in proportions of 1 ml, 3 ml and 5 ml. The experimental study was carried out on a single cylinder DI diesel engine. The result showed an appreciable reduction of emissions such as smoke density, particulate matter and marginal increase in the performance when compared with normal diesel run. The same engine was employed with diesel particulate trap (DPT) in the exhaust pipe to study its influence on the emission analysis.     

Experimental study on particulate emission of a diesel engine fueled with blended ethanol–dodecanol–diesel

Experiments were conducted on a 4-cylinder direct-injection diesel engine which has a compressing ratio of 19, using ultra low sulfur diesel blended with ethanol using 1–1.5% by volume of 1-dodecanol as the solvent to investigate the particulate emissions of the engine under five engine loads and at engine speeds of 1800 and 2400 rev/min. Blended fuels containing 6.1%, 12.2%, 18.2% and 24.2% by volume of ethanol, corresponding to 2%, 4%, 6% and 8% by mass of oxygen in the blended fuel, were used. At both engine speeds, with an increase in ethanol in the fuel, the smoke opacity, the particulate mass concentration and the total number of nano-size particles are all reduced. A diesel oxidation catalyst (Finnkat) was used and found to further reduce particulate emission. The smoke opacity, the particulate mass concentration and the total number concentration at 2400 rev/min are higher than those at 1800 rev/min.     

Transient testing of soy methyl ester fuels in an indirect injection,compression ignition engine

An evaluation of the exhaust emissions from a compression ignition engine for fuels composed of 100 and 30% methyl esters of soy oil (SME) is described. These fuels were compared with a low-sulfur, petroleum #2 diesel fuel in a Caterpillar 3304, prechamber, 75 kW diesel engine, operated over heavy- and light-duty transient test cycles developed by the United States Bureau of Mines. More than 60 h of testing was performed on each fuel. The objective was to determine the influence of the fuels upon diesel particulate matter (DPM) and gaseous emissions. The effect of a modern diesel oxidation catalyst (DOC) also was determined in an effort to minimize emissions. Neat SME produced a higher volatile fraction of the DPM, but much less carbon soot fraction, leading to overall DPM reductions of 23 to 30% for the light- and heavy-duty transients. The DOC further reduced the volatile fraction and the total DPM. The SME fuel reduced gaseous emissions of CO by 23% and hydrocarbons by over 30% without increasing NO_x. The DOC further reduced CO and hydrocarbon levels. Mutagenicity of the SME exhaust was low. Results indicate that SME fuel, used with a proper DOC, may be a feasible emission reduction technology for underground mines. References to specific products do not imply endorsement by the U.S. Bureau of Mines, a now defunct agency.     

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.     

Experimental investigation on particulate emissions of a direct injection diesel engine fueled with diesel–diethyl adipate blends

Euro V diesel fuel blended with 8.1%, 16.4%, 25% and 33.8% by volume of diethyl adipate (DEA), corresponding to 3%, 6%, 9% and 12% by mass of oxygen in the blended fuels, were tested on a 4-cylinder direct-injection diesel engine. Experiments were conducted under five engine loads at a steady speed of 1800 rev/min to investigate the effects of the blended fuels on combustion and particulate emission characteristics. The results indicate an increase in ignition delay and the amount of heat release in the premixed burning phase, while a decrease in both diffusive and total combustion duration with an increase in DEA in the fuel. Compared to the diesel fuel, the particulate mass concentration and the total number of particles are reduced significantly, whereas the proportion of soluble organic fraction (SOF) in the particles increases with increasing DEA in the fuel. The increase in SOF might increase the toxicity of the particles. Moreover, the geometric mean diameter (GMD) of the particles shifts towards smaller size. A diesel oxidation catalyst was used and found to further reduce both particulate mass and total number concentration. The results also show that the DOC could reduce the finer particles more effectively.     

Aviation fuel JP-5 and biodiesel on a diesel engine

Naval aviation turbine fuel, JP-5, has been accepted as alternative to JP-8 in the frame of the Single Fuel Policy. This has resulted in some ongoing research on JP-5 fuel for its application as a naval single fuel. The necessity to cope with the environmental problems identified in the process of implementing the Single Fuel Policy as well as the strict requirements of modern diesel engines has lead to the need of improved single fuel quality. The development of biomass derived substitutes for diesel, such as biodiesel, is a possible attractive solution. The present paper is an effort to evaluate JP-5 along with diesel and biodiesel for use in a diesel engine. These fuels were used alone and in various mixture fractions in a single cylinder stationary diesel engine in order to evaluate their performance under defined operating conditions of the engine. JP-5 reduced both the NOx and particulate matter emissions as compared to the reference fuel case. Biodiesel significantly lowered particulate emissions, but slightly increased NOx emissions and fuel consumption. Fuel sulfur content has an undesired effect on smoke opacity. Biodiesel increased the fuel consumption when added to petroleum fuels and the increase was larger at high engine loads. Diesel and JP-5 showed similar fuel consumption, with diesel consumption increasing at high engine loads. Ternary blends showed similar behavior. The blends with lower biodiesel content showed lower volumetric fuel consumption.     

Oxygenated blend design and its effects on reducing diesel particulate emissions

In order to meet Euro IV emission standards, diesel vehicles are compelled to install exhaust aftertreatment devices, which largely increases the overall cost. This paper explores the possibility to significantly reduce the particulate matter (PM) emissions by new fuel design. Several oxygenated blends were obtained by mixing the biodiesel, ethanol, dimethyl carbonate (DMC), and diesel fuels. The tests were conducted on two heavy-duty diesel engines, both with a high-pressure injection system and a turbocharger. The total PM and its dry soot (DS) and soluble organic fraction (SOF) constituents were analyzed corresponding to their specific fuel physiochemical properties. A blended fuel that contains biodiesel, DMC, and high cetane number diesel fuels was chosen eventually to enable the diesel engines to meet the Euro IV emission regulation. Based on the test results, the basic design principles were derived for the oxygenated blends that not only need the high oxygen content, but also the high cetane number and the low sulfur and low aromatic contents.     

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     

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.     

Flow properties of biodiesel fuel blends at low temperatures

The dynamic viscosities of biodiesel derived from ethyl esters of fish oil, no. 2 diesel fuel, and their blends were measured from 298 K down to their respective pour points. Blends of B80 (80 vol.% biodiesel–20 vol.% no. 2 diesel), B60, B40 and B20 were investigated. All the viscosity measurements were made with a Bohlin VOR Rheometer. Cloud point and pour point measurements were made according to ASTM standards. Arrhenius equations were used to predict the viscosities of the pure Biodiesel (B100), no. 2 diesel fuel (B0) and the biodiesel blends (B80, B60, B40, and B20) as a function of temperature. The predicted viscosities agreed well with measured values. An empirical equation for calculating the dynamic viscosity of these blends as a function of both temperature and blend has been developed. Furthermore, based on the kinematic viscosity and density measurements of B100 up to 573 K by Tate et al. [Tate RE, Watts KC, Allen CAW, Wilkie KI. The viscosities of three biodiesel fuels at temperatures up to 300 °C. Fuel 2006;85:1010–5; Tate RE, Watts KC, Allen CAW, Wilkie KI. The densties of three biodiesel fuels at temperatures up to 300 °C. Fuel 2006;85:1004–9] an empirical equation for predicting the dynamic viscosity of pure biodiesel for temperatures from 277 K to 573 K is given. Empirical equations for predicting the cloud and pour point for a given blend give values in good agreement with experiments. The dynamic viscosity of biodiesel and its blends increases as temperature decreases and show Newtonian behaviour down to the pour point. Dynamic viscosity, cloud point and pour point decreases with an increase in concentration of no. 2 diesel in the blend.     

Combustion characteristics of waste-oil produced biodiesel/diesel fuel blends

In this study, wasted cooking oil from restaurants was used to produce neat (pure) biodiesel through transesterification, and this converted biodiesel was then used to prepare biodiesel/diesel blends. The goal of this study was to compare the trace formation from the exhaust tail gas of a diesel engine when operated using the different fuel type: neat biodiesel, biodiesel/diesel blends, and normal diesel fuels. B20 produced the lowest CO concentration for all engine speeds. B50 produced higher CO₂ than other fuels for all engine speeds, except at 2000 rpm where B20 gave the highest. The biodiesel and biodiesel/diesel blend fuels produced higher NO_x for various engine speeds as expected. SO₂ formation not only showed an increasing trend with increased engine speed but also showed an increasing trend as the percentage of diesel increased in the fuels. Among the collected data, the PM concentrations from B100 engines were higher than from other fuelled engines for the tested engine speed and most biodiesel-contained fuels produced higher PM than the pure diesel fuel did. Overall, we may conclude that B20 and B50 are the optimum fuel blends. The species of trace formation in the biodiesel-contained fuelled engine exhaust were mainly C_nH_2n+2, DEP, and DPS. For the B100, B80, B50, and D fuelled engines, C₁₅H₃₂ was the dominant species for all engine speeds, while squalene (C₃₀H₅₀) was the dominant for B20. DEP was only observed in the B100, B80, and B50 fuelled engines in this study. The D fuelled engine showed a higher DPS production for engine speeds higher than 1200 rpm.     

Emission characteristics of diesel, gas to liquid, and biodiesel-blended fuels in a diesel engine for passenger cars

The need for diversification of energy sources and reducing various emissions including CO₂ emission in diesel engine can be met with alternative diesel fuels such as gas to liquid (GTL) and GTL–biodiesel blends. But there should be a clear understanding of the combustion and engine-out emission characteristics for alternative fuels. In this respect, an experimental study was conducted on a 2.0 L 4 cylinders turbocharged diesel engine fuelled with those alternative diesel fuels to investigate the engine-out emission characteristics under various steady-state engine operating conditions. The results revealed that noticeable decreases in THC (22–56%) and CO (16–52%) emissions for GTL–biodiesel blends were observed, whereas NOx emissions for GTL–biodiesel blends increased by a maximum of 12% compared to diesel. With regard to particle size distributions (PSDs) for GTL–biodiesel blends, the particulate matter (PM) number concentration in accumulation mode decreased, as a result of the excess oxygen content in biodiesel. Contrary to the tendency in the accumulation mode, there was a slight increase in the PM number concentration in the nucleation mode under the operating conditions wherein the exhaust gas recirculation (EGR) strategy was applied. The total PM number concentration for G + BD40 decreased by a maximum of 46% compared to that for diesel. From these results of enhanced emission characteristics compared to diesel and GTL fuel, the potential for the use of GTL–biodiesel blends could be confirmed.     

Effects of emulsification variables on fuel properties of two- and three-phase biodiesel emulsions

Biodiesel has attractive fuel properties such as excellent biodegradability and lubricity, almost no emissions of sulfur oxides, PAH and n-PAH, reduced CO₂, PM and CO emission, superior combustion efficiency, etc. However, burning of biodiesel generally produces higher levels of NO_x emissions, primarily due to its high oxygen content. In this study, the emulsification technology has been considered to reduce the NO_x emission level of fossil fuel. Biodiesel, produced by means of transesterification reaction accompanied with a peroxidation process, was emulsified to form two-phase W/O and three-phase O/W/O emulsions. The effects of the emulsification variables such as hydrophilic lipophilic balance (HLB), and water content on the fuel properties and emulsion characteristics of W/O and O/W/O emulsions were investigated in this study. The experimental results show that the surfactant mixture with HLB = 13 produced the highest emulsification stability while HLB = 6 produced the lowest emulsification stability and the most significant extent of water–oil separation among the various HLB values for O/W/O biodiesel emulsion. The kinematic viscosity, specific gravity and carbon residual of the biodiesel emulsions were larger than those of the neat biodiesel. In addition, the W/O biodiesel emulsion was found to have a smaller mean droplet size, lower volumetric fraction of the dispersed phase than the O/W/O biodiesel emulsion, and the highest heating value among the test fuels, if the water content is deducted from the calculation of the heating value.     

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.     

Comparison of exhaust emissions and their mutagenicity from the combustion of biodiesel, vegetable oil, gas-to-liquid and petrodiesel fuels

Efforts are under way to reduce diesel engine emissions (DEE) and their content of carcinogenic and mutagenic polycyclic aromatic hydrocarbons (PAH). Previously, we observed reduced PAH emissions and DEE mutagenicity caused by reformulated or newly developed fuels. The use of rapeseed oil as diesel engine fuel is growing in German transportation businesses and agriculture. We now compared the mutagenic effects of DEE from rapeseed oil (RSO), rapeseed methyl ester (RME, biodiesel), natural gas-derived synthetic fuel (gas-to-liquid, GTL), and a reference petrodiesel fuel (DF) generated by a heavy-duty truck diesel engine using the European Stationary Cycle. Mutagenicity of the particle extracts and the condensates was tested using the Salmonella typhimurium mammalian microsome assay with strains TA98 and TA100. The RSO particle extracts increased the mutagenic effects by factors of 9.7 up to 17 in strain TA98 and of 5.4 up to 6.4 in strain TA100 compared with the reference DF. The RSO condensates caused up to three times stronger mutagenicity than the reference fuel. RME extracts had a moderate but significantly higher mutagenic response in assays of TA98 with metabolic activation and TA100 without metabolic activation. GTL samples did not differ significantly from DF. Regulated emissions (hydrocarbons, carbon monoxide, nitrogen oxides (NO_x), and particulate matter) remained below the limits except for an increase in NO_x exhaust emissions of up to 15% from the tested biofuels.     

Study of oxygenated biomass fuel blends on a diesel engine

Vegetable methyl ester was added in ethanol–diesel fuel to prevent separation of ethanol from diesel in this study. The ethanol blend proportion can be increased to 30% in volume by adding the vegetable methyl ester. Engine performance and emissions characteristics of the fuel blends were investigated on a diesel engine and compared with those of diesel fuel. Experimental results show that the torque of the engine is decreased by 6%–7% for every 10% (by volume) ethanol added to the diesel fuel without modification on the engine. Brake specific fuel consumption (BSFC) increases with the addition of oxygen from ethanol but equivalent brake specific fuel consumption (EBSFC) of oxygenated fuels is at the same level of that of diesel. Smoke and particulate matter (PM) emissions decrease significantly with the increase of oxygen content in the fuel. However, PM reduction is less significant than smoke reduction. In addition, PM components are affected by the oxygenated fuel. When blended fuels are used, nitrogen oxides (NO_x) emissions are almost the same as or slightly higher than the NO_x emissions when diesel fuel is used. Hydrocarbon (HC) is apparently decreased when the engine was fueled with ethanol–ester–diesel blends. Fuelling the engine with oxygenated diesel fuels showed increased carbon monoxide (CO) emissions at low and medium loads, but reduced CO emissions at high and full loads, when compared to pure diesel fuel.     

Influence of waste cooking oil biodiesel on the nanostructure and volatility of particles emitted by a direct-injection diesel engine

To reduce air pollution and the reliance on fossil fuel, biodiesel has been widely investigated as an alternative fuel for diesel engines. The purpose of this study is to investigate the influence of waste cooking oil (WCO) biodiesel on the physical properties and the oxidation reactivity of the particles emitted by a diesel engine operating on WCO biodiesel as the main fuel. Experiments were conducted on a direct-injection diesel engine fueled with biodiesel, B75 (75% biodiesel and 25% diesel on volume basis, v/v), B50, B20, and diesel fuel, at five engine loads and at an engine speed of 1920 rev/min. Particulate samples were collected to analyze the particulate nanostructure, volatility, and oxidation characteristics. Biodiesel or low-load operation leads to smaller primary particles and more disordered nanostructures having shorter and more curved graphene layers. It can be found that particles from biodiesel, blended fuels, or low-load operation have higher volatile mass fractions and faster oxidation reaction rates than particles from diesel or heavy-load operation. The higher oxidation reaction rates are due mainly to the smaller particle size, the more disordered nanostructure, and the higher volatile mass fraction. It is also found that changes in primary particle size and particulate nanostructure are not directly proportional to the biodiesel content, while changes in particulate volatility and particulate oxidation reactivity are proportional to the biodiesel content. The use of biodiesel can enhance particulate oxidation reactivity and the regeneration of soot particles in an after-treatment device.

Copyright © 2016 American Association for Aerosol Research     

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.