Search

Fast pyrolysis bio-oils are completely different from petroleum fuels and other bio-fuels available in the market, as regards both to their physical properties and chemical composition. When the unusual properties of these bio-oils are carefully taken into account in system and burner design, their combustion without a pilot flame or support fuel is possible on an industrial scale. The aim of the paper is to review the work done on combustion of fast pyrolysis bio-oils and highlight the latest and most important findings of its combustion from laboratory fundamentals to industrial scale. The main focus of the paper is on the bio-oil burner applications.In recent industrial scale bio-oil combustion tests, bio-oil has been found to be technically suitable for replacing heavy fuel oil in district heating. In addition, it has also been found out that limited possibilities for further lowering particulate emissions exist, since the majority of the particulates are typically incombustible matter. Curves for NO. x-emissions of fast pyrolysis bio-oil combustion for air-assisted atomization burners are presented in the paper.Current burner designs are quite sensitive to the changes in the quality of the bio-oil, which may cause problems in ignition, flame detection and flame stabilization. Therefore, in order to be able to create reliable bio-oil combustion systems that operate at high efficiency, bio-oil grades should be standardized for combustion applications. Careful quality control, combined with standards and specifications, all the way from feedstock harvesting through production to end-use is recommended in order to make sure that emission targets and limits in combustion applications are achieved. Also the cost-effectiveness of the total package is extremely important.

Exhaust gas particle and ion size distributions were measured from an off-road diesel engine complying with the European Stage IIIB emission standard. The measurements were performed at idling and low load conditions on an engine dynamometer. Nucleation-mode particles dominated the diesel exhaust particle number emissions at idle load. The nonvolatile nucleation-mode geometric mean diameter was detected at 10 nm or below. The nonvolatile nucleation-mode charge state implied that it has evolved through a highly ionizing environment before emission from the engine. The determined charging probabilities were 10.0 ± 2.2% for negative and 8.0 ± 2.0% for positive polarity particles. The nonvolatile nucleation particle concentration and size was also shown to be dependent on the lubricant oil composition. The particle emissions were efficiently controlled with a partial filter or with partial filter + selective catalytic reduction (SCR) combination. The particle number removal efficiencies of the aftertreatment systems were over 95% for wet total particle number (>3nm) and over 85% for dry particle total number. Nevertheless, the aftertreatment systems’ efficiencies were around 50% for the soot-mode particles. The low-load nonvolatile nucleation particle emissions were also dependent on the engine load, speed, and fuel injection pressure. The low load particle number emissions followed the soot-core trade-off, similar to medium or high operating loads.

The effects of the fuel injection pressure on a heavy-duty diesel engine exhaust particle emissions were studied. Nonvolatile particle size distributions and gaseous emissions were measured at steady-state engine conditions while the fuel injection pressure was changed. An increase in the injection pressure resulted in an increase in the nonvolatile nucleation mode (core) emission at medium and at high loads. At low loads, the core was not detected. Simultaneously, a decrease in soot mode number concentration and size and an increase in the soot mode distribution width were detected at all loads. Interestingly, the emission of the core was independent of the soot mode concentration at load conditions below 50%. Depending on engine load conditions, growth of the geometric mean diameter of the core mode was also detected with increasing injection pressure. The core mode emission and also the size of the mode increased with increasing NOx emission while the soot mode size and emission decreased simultaneously.

Heavy duty diesel engine exhaust characteristics were studied with direct tailpipe sampling on an engine dynamometer. The exhaust particle size distributions, total particle mass, and gaseous emissions were measured with different load conditions without after-treatment. The measured particle size distributions were bimodal; distinctive accumulation and nucleation modes were detected for both volatile and dry particle samples. The condensing volatile compounds changed the characteristics of the nonvolatile nucleation mode while the soot/accumulation mode characteristics (concentration and diameter) were unchanged. A clear dependence between the soot and the nonvolatile nucleation mode number concentrations was detected. While the concentration of the soot mode decreased, the nonvolatile nucleation mode concentration increased. The soot mode number concentration decrease was related to soot-NOx trade-off; the decrease of the exhaust gas recirculation rate decreased soot emission and increased NOx emission. Simultaneously detected increase of the nonvolatile nucleation mode concentration may be caused by the decrease of the soot mode sink or by changed combustion characteristics. However, the total particle number concentration increased with decreasing soot mode number concentration. The proportion of the particle number concentration between the nonvolatile nucleation and soot mode followed the NO2:NO ratio linearly. While ratio NO2:NO increased the proportion of soot mode number concentration in total number concentration increased. Regardless of the mechanism that causes the balance between the soot mode and the nonvolatile nucleation mode emissions, the changes in the particle number size distribution should be taken into account while the particle mass emissions are controlled with combustion optimization.

Combustion properties of various pyrolysis oils were studied at Oilon (Lahti, Finland) in a test boiler on 4 MW output level. Burner settings and boiler dimensions as well as oil properties were tested. A special emphasis was on oil specifications for boiler application. It was concluded that pyrolysis oils can be combusted in slightly modified conventional oil furnaces and boilers fairly well. Some existing oil burners are also capable to combust pyrolysis oils, but they might need slight modification. However, oil specifications must be defined, including at least water and solids. Special care should be taken in handling and pumping of oils. Support fuel is needed at the burner to start the combustion and recommended for supporting pyrolysis oil in case of poor-quality oil. Emissions depend on oil quality. They are generally equal to those of light fuel oil or light bunker oil, but the content of particles in exhaust gases is higher. The results are applicable with small modifications in the boiler size class down to 1 MWth. Research into replacing light fuel oil in boilers below 1 MWth continues.

Effect of lubricant on particle emissions was studied using two heavy-duty diesel engines. Both particulate mass and particle number distribution were measured. Differences between lubricants were studied by dosing two percent of each lubricant (diesel engine oil) to diesel fuel. This arrangement was seen necessary to get clear differences between lubricants. The lubricant had a clear effect on particulate mass emissions. Two of the lubricants gave about the same emission as pure diesel fuel. The worst result was more than two times higher than without oil added to the fuel. The lubricants were all diesel engine oils with different base oils/additive package. Lubricant ash content presumably affects particulate mass. However, the difference in ash content between lubricants was no higher than 30%. Therefore, ash content can only partly explain the differences. The combustion characteristics and the sulphur content of the base oil are essential, too. All fuels containing lubricant produced higher number of small particles than pure diesel fuel. The lubricant, which gave the lowest particulate mass result, produced the highest number of particles. The reason might be that when the number of large particles decreases (also particle mass decreases), the small particles cannot agglomerate to the surfaces of larger particles. It is also possible that, for example, oxidation of catalyst could reduce the number of small particles.

The purpose of our study was to investigate the effects of TAME and heavier ethers on reformulated gasoline. The research work focused on the comparison of Californian Phase 2 gasoline (CARB), current Finnish reformulated gasoline containing MTBE (RFG1), or MTBE+TAME+heavier ethers (RFG2) with non-oxygenated Eurograde gasoline (EN228). Significant reductions in exhaust emissions were achieved with all reformulated fuels when compared to the Eurograde fuel. For instance, benzene emissions were reduced as much as 40 to 50 % for all cars at two temperatures and the emissions of total toxics were reduced by 14 to 45 % depending on vehicle type and temperature. The lowest 1,3-butadiene emissions were achieved with CARB gasoline. The amount of PAH compounds in the particulate matter from the non-catalyst vehicle was lower with the reformulated fuels than with the Eurograde fuel. The amount of volatile PAH compounds in semivolatile phase of particles seemed to be reduced with reformulated gasoline as well. As gasoline blending components TAME and heavier ethers proved to be as good as MTBE. Additionally they improved the octane number distribution of reformulated gasolines.

This paper presents the results of a gasoline reformulation project carried out in Finland during 1993. The project focused on the impact of gasoline sulfur and benzene content on exhaust emissions. Twelve 1990 - 1993 model vehicles were tested using two fuel sulfur levels, 500 and 100 ppm, and two benzene levels, 1 wt.% and 3 wt.%. Another subject of investigation was evaporative emissins during refuelling. When the sulfur content of the fuel was reduced from 500 to 100 ppm, the regulated exhaust emissions from catalyst cars decreased at test temperatures 22°C as follows: carbon monoxide CO 14%, total hydrocarbons THC 7% and nitrogen oxides NOx 9%. At test temperatures -7°C the reduction of sulfur content gave smaller benefits expressed in percentages, but the absolute changes (g/km) were at the same level as at +22°C. When the benzene content of the gasoline was decreased from 3 wt.% to 1 wt.%, the benzene emissions of cars were reduced by 20 - 30 % both at test temperatures 22°C and at test temperatures -7°C. Total hydrocarbons and benzene evaporation was determined during refuelling. Total HC decreased in direct proportion to a 24 percent reduction in vapor pressure. Benzene evaporation decreased two thirds when low benzene fuel was used.

Propane is considered to be a viable fuel alternative for low-emission heavy-duty vehicles in Finland. Natural gas and propane have roughly the same potential for reduced exhaust emissions. Since natural gas and propane are both imported fuels in Finland, there is no preference between these two fuels. Propane, however, is much more easy to distribute, refuel and store onboard the vehicle. This is why propane has received more attention than natural gas as an automotive fuel.Work to develop a low-emission propane fueled truck started back in 1988 with engine tests. The first prototype, a 17-ton SISU truck was built in 1990, and was operated until September 1992. This truck was equipped with a 7.4-liter Valmet-engine, a closed-loop controlled IMPCO-fuel system and a three-way catalytic converter (TWC).The experience with this propane fueled truck was good. The driveability was excellent, and both noise level and exhaust emissions were low. The following emission results were obtained in the European 13-mode (ECE R49) emission test with a three-way catalyst aged for 30.000 km: CO 1.8, THC 0.5 and NOx 0.5 g/kWh.Encouraged by these good results the Finnish truck manufacturer Oy Sisu-Auto Ab decided to build a test fleet of seven propane fueled trucks. These trucks were built in late 1992/early 1993. One of these trucks is used for test and demonstration purposes, and six trucks have been delivered to five different operators for various applications like municipal waste collection, distribution work and street maintenance. A surveillance program concerning these trucks is currently under way.In the years 1990-1993 a surveillance project on a propane fueled MAN-citybus was carried out concurrent with the truck operations. This vehicle also uses TWC technology. The surveillance work included both weekly checkups on the fuel system and catalysts. Furthermore, altogether six measurements were carried out on a chassis dynamometer according to a modified ECE R49 procedure.In April 1993 the total accumulated driving distance was some 200.000 km and the bus has worked relatively well, although some minor technical problems have occurred. Judged by the emission test, the original catalyst had lost 50% of its efficiency at 80.000 km. This catalyst was then replaced with a converter from the Finnish company Kemira Oy. With this new catalyst, extremely low emission values were obtained.

This paper presents the results of a gasoline reformulation project carried out in Finland during 1991. The target was to evaluate MTBE and ETBE as gasoline components with respect to operability and exhaust emission performance. The oxygenated fuels contained 2 to 2.7 per cent oxygen by weight. The oxygenated fuels reduced exhaust emissions significantly at normal ambient temperature. For non-catalyst cars the reduction of CO was 15 to 30 % and the reduction of HC was approx. 5 %. For three way catalyst (TWC) cars the CO emission decrease varied from 0 to 10 % and HC approx. 10 %. The use of oxygenates reduced exhaust emissions also at low ambient temperature, but not as much as at normal temperature. Cold starting was quicker and cold driveability was better when oxygenated fuels were used.

Properties of various gear lubricants were studied in the temperature range of +20 - -40 °C. The tests were carried out in the cold research facilities of the Laboratory of Fuel and Process Technology of the Technical Research Centre of Finland (VTT) using the gearbox of a rear wheel drive delivery van as the test equipment. The tests focused solely on the gear and its lubrication. The output shaft of the gearbox was connected directly to the engine dynamometer and the input shaft was rotated by a hydraulic motor.The aim of the tests was to study the properties of different lubricants in the gearbox at cold-start and start. The most significant reading monitored was the power loss in the gearbox as a function of time. This affects the fuel consumption of the vehicle. The warming-up of the lubricant was also measured, as well as possible changes in the viscosity over the test.The efficiency of the gearbox increased in five minutes close to the final value of the 40 min test. The power loss (efficiency) at the start-up can be affected by the choice of the lubricant, although lubricants cannot be classified solely by the viscosity class under the coldest conditions. In these tests, in which the load was equal to that of drive at a constant speed of about 80 km/h, the power demand was increased by a poorly flowing lubricant not more than by 5 - 6 % during the first five minutes.The test temperature had a fairly great effect on the stabilized power loss in the gearbox. For example, the difference between the power losses at the temperatures of -26 °C and +20 °C was on average 0.8 kW, about 5 %.

Simulated start-up tests were made in a cold chamber with two gasoline-fueled four-cylinder passenger car engines. The engine was motored with a hydraulic motor according to a certain test programme. The time required for the oil pressure to build up was measured on the camshaft bearing which is the most remote point of the lubrication system. The oil pressure in the smaller engine was also measured before and after the oil filter. The torque required for motoring the engine and the temperature of the oil, one main bearing and one camshaft bearing were also measured, in addition to the motoring tests, start-up tests were made with the other engine to get information about the correlation of the motoring test results with a start-up situation in practice. At ambient temperatures < 20 °C there were differences especially in the pumpability properties of oils even within the same viscosity class. Hence, the choice of oil and the use of auxiliary heaters are of great significance.