Diesel and rapeseed methyl ester (RME) pilot fuels for hydrogen and natural gas dual-fuel combustion in compression-ignition engines

This paper presents experimental results of rapeseed methyl ester (RME) and diesel fuel used separately as pilot fuels for dual-fuel compression-ignition (CI) engine operation with hydrogen gas and natural gas (the two gaseous fuels are tested separately). During hydrogen dual-fuel operation with both pilot fuels, thermal efficiencies are generally maintained. Hydrogen dual-fuel CI engine operation with both pilot fuels increases NO_x emissions, while smoke, unburnt HC and CO levels remain relatively unchanged compared with normal CI engine operation. During hydrogen dual-fuel operation with both pilot fuels, high flame propagation speeds in addition to slightly increased ignition delay result in higher pressure-rise rates, increased emissions of NO_x and peak pressure values compared with normal CI engine operation. During natural gas dual-fuel operation with both pilot fuels, comparatively higher unburnt HC and CO emissions are recorded compared with normal CI engine operation at low and intermediate engine loads which are due to lower combustion efficiencies and correspond to lower thermal efficiencies. This could be due to the pilot fuel failing to ignite the natural gas-air charge on a significant scale. During dual-fuel operation with both gaseous fuels, an increased overall hydrogen-carbon ratio lowers CO₂ emissions compared with normal engine operation. Power output (in terms of brake mean effective pressure, BMEP) as well as maximum engine speed achieved are also limited. This results from a reduced gaseous fuel induction capability in the intake manifold, in addition to engine stability issues (i.e. abnormal combustion). During all engine operating modes, diesel pilot fuel and RME pilot fuel performed closely in terms of exhaust emissions. Overall, CI engines can operate in the dual-fuel mode reasonably successfully with minimal modifications. However, increased NO_x emissions (with hydrogen use) and incomplete combustion at low and intermediate loads (with natural gas use) are concerns; while port gaseous fuel induction limits power output at high speeds.     

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.     

Performance, combustion and emissions of a diesel engine operated with reformed EGR. Comparison of diesel and GTL fuelling

In this work, the effects of a standard ultra-low sulphur diesel (ULSD) fuel and a new, ultra-clean synthetic GTL (gas-to-liquid) fuel on the performance, combustion and emissions of a single-cylinder, direct injection, diesel engine were studied under different operating conditions with addition of simulated reformer product gas, referred to as reformed EGR (REGR). For this purpose various levels of REGR of two different compositions were tested. Tests with standard EGR were also carried out for comparison. Experiments were performed at four steady state operating conditions and the brake thermal efficiency, combustion process and engine emission data are presented and discussed. In general, GTL fuel resulted in a higher brake thermal efficiency compared to ULSD but the differences depended on the engine condition and EGR/REGR level and composition. The combustion pattern was significantly modified when the REGR level was increased. Although the extent of the effects of REGR on emissions depended on the engine load, it can be generally concluded that an optimal combination of GTL and REGR significantly improved both NO_x and smoke emissions. In some cases, NO_x and smoke emission reductions of 75% and 60%, respectively, were achieved compared to operation with ULSD without REGR. This offers a great potential for engine manufacturers to meet the requirements of future emission regulations.     

Experimental investigation of mineral diesel fuel, GTL fuel, RME and neat soybean and rapeseed oil combustion in a heavy duty on-road engine with exhaust gas aftertreatment

The effects of mineral diesel fuel, gas-to-liquid fuel, rapeseed methyl ester, neat soybean and neat rapeseed oil on injection, combustion, efficiency and pollutant emissions have been studied on a compression ignition heavy duty engine operated near full load and equipped with a combined exhaust gas aftertreatment system (oxidation catalyst, particle filter, selective catalytic NO_x reduction). In a first step, the engine calibration was kept constant for all fuels which led to differences in engine torque for the different fuels. In a second step, the injection duration was modified so that all fuels led to the same engine torque. In a third step, the engine was recalibrated in order to keep the NO_x emissions at an equal level for all fuels (injection pressure, injection timing, EGR rate). The experiments show that the critical NO_x emissions were higher (even behind the exhaust gas aftertreatment systems) for oxygenated fuels in case of the engine not being recalibrated for the fuel. GTL and the oxygenated fuels show lower emissions for some pollutants and higher efficiency after recalibration to equal NO_x levels.     

Studies on improving the performance of rubber seed oil fuel for diesel engine with DEE port injection

Use of vegetable oils in diesel engines leads to a marginally inferior performance and higher smoke emissions due to their high viscosity and carbon residue. The performance of vegetable oils can be improved by injecting a small quantity of diethyl ether (DEE) along with air. The main objective of this study is to improve the performance, emission and combustion characteristics of a direct injection diesel engine fuelled with rubber seed oil (RSO) through DEE injection at different flow rates of 100, 150 and 200 g/h. A single cylinder diesel engine with rated output of 4.4 kW at 1500 rpm was converted to operate in the DEE injection mode. DEE was injected into the intake port during suction stroke, while rubber seed oil was injected directly inside the cylinder at the end of compression stroke. The injection timing of DEE was optimized for this mode of operation. Results indicate that the brake thermal efficiency of the engine improves from 26.5% with neat RSO to a maximum of 28.5% with DEE injection rate of 200 g/h. Smoke reduces from 6.1 to 4 BSU with DEE injection at the maximum efficiency flow rate. Hydrocarbon and carbon monoxide emissions are also less with DEE injection. There is an increase in the NO_x emission from 6.9 g/kWh to 9.3 g/kWh at the optimum DEE flow rate. DEE injection with RSO shows higher peak pressure and rate of pressure rise compared to neat RSO. Heat release rate indicates an increase in the combustion rate due to the reduced ignition delay and combustion duration with DEE injection.     

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.     

Experimental investigation on a C.I. engine using orange oil and orange oil with DEE

In the present work, the effect of using neat orange oil, optimum orange oil-diesel blend and the optimum flow rate of DEE with orange oil are evaluated for the performance, emissions and combustion characteristics of a single cylinder, diesel engine. The experimental results show that carbon monoxide (CO), hydrocarbon (HC) and smoke emissions decrease while oxides of nitrogen (NO_x) emissions increase for orange oil and its blends compared to diesel fuel and DEE with orange oil. The brake thermal efficiency in the case of DEE with orange oil is higher than that of orange oil, orange oil-diesel fuel blend and diesel fuel. The peak cylinder pressure and heat release rate for DEE with orange oil are higher than those of diesel fuel operation.     

Effects of biodiesel on a DI diesel engine performance, emission and combustion characteristics

Experimental tests were investigated to evaluate the performance, emission and combustion of a diesel engine using neat rapeseed oil and its blends of 5%, 20% and 70%, and standard diesel fuel separately. The results indicate that the use of biodiesel produces lower smoke opacity (up to 60%), and higher brake specific fuel consumption (BSFC) (up to 11%) compared to diesel fuel. The measured CO emissions of B5 and B100 fuels were found to be 9% and 32% lower than that of the diesel fuel, respectively. The BSFC of biodiesel at the maximum torque and rated power conditions were found to be 8.5% and 8% higher than that of the diesel fuel, respectively. From the combustion analysis, it was found that ignition delay was shorter for neat rapeseed oil and its blends tested compared to that of standard diesel. The combustion characteristics of rapeseed oil and its diesel blends closely followed those of standard diesel.     

Characteristics of polycyclic aromatic hydrocarbons emissions of diesel engine fueled with biodiesel and diesel

With mutagenic and carcinogenic potential, polycyclic aromatic hydrocarbons (PAHs) from mobile source exhaust have contributed to a substantial share of air toxics. In order to characterize the PAHs emissions of diesel engine fueled with diesel, biodiesel (B100) and its blend (B20), an experimental study has been carried out on a direct-injection turbocharged diesel engine. The particle-phase and gas-phase PAHs in engine exhaust were collected by fiberglass filters and “PUF/XAD-2/PUF” cartridges, respectively, then the PAHs were determined by a gas chromatograph/mass spectrometer (GC/MS). The experimental results indicated that comparing with diesel, using B100 and B20 can greatly reduce the total PAHs emissions of diesel engine by 19.4% and 13.1%, respectively. The Benzo[a]Pyrene (BaP) equivalent of PAHs emissions were also decreased by 15.0% with the use of B100. For the three fuels, the gas-phase PAHs emissions were higher than particle-phase PAHs emissions and the most abundant PAH compounds from engine exhaust were naphthalene and phenanthrene. The analysis showed that there was a close correlation between total PAHs emissions and particulate matter (PM) emissions for three fuels. Furthermore, the correlation became more significant when using biodiesel.     

Emission Reduction of Regenerative Fuel Powered Co-Generation Plants with SCR- and Oxidation-Catalysts

Since the beginning of combustion engine development in this recent century various different fuels have been successfully tested. Diesel engines have been adapted to fuels made from mineral oils because of the rising importance and the cheapness in comparison to other fuels. On the other hand, it is possible to burn regenerative fuels in engines and achieve some significant advantages in comparison to fossil diesel fuel. This is, for example, a closed carbon dioxide (CO₂) cycle which causes no green house effect. It is possible to extract oil from various seeds like rapeseed. It is also possible to burn used oil from the food processing industry or waste grease and oil from food recycling companies. The great advantages: (1) food recycling oils can produce energy instead of use as animal food, and (2) as nobody knows exactly the consistency of the collected oils, poisonous pollution is possible. These regenerative fuels can be burned without any further processing in special adapted diesel engines, for example an Elsbett engine, or in precombustion engines with large swept volumes. Most researchers focused on operating diesel engines with regenerative fuels and reducing the emissions caring only about regulated exhaust components. In comparison to these studies it is necessary to learn more about the emissions beyond the exhaust regulations. Additionally emission reduction is possible by using an SCR-catalyst (selective catalytic reduction) to reduce the NO₂ combined with an oxidation-catalyst which reduces any kind of oxidisable emissions. The TU München, Lehrstuhl für Energie- und Umwelttechnik der Lebensmittelindustrie, operates a small co-generation plant with the ability of analysing the standard emission components (CO, NO₂, HC, particles, CO₂, O₂) and unregulated components (SO₂, NH₃, polycyclic aromatic hydrocarbons (PAH), aldehyde, ketone). The emissions show some significant differences in comparison to fossil diesel fuel which is caused by the diversity of each fuel. Results of an investigation on four different fuels (wastefat methyl ester (WME), rapeseed methyl ester (RME), rapeseed oil and diesel fuel) burned in a small co-generation plant with a SCR- and oxidation-catalyst will be presented. A comparison to the emissions before and after the catalysts will be shown additionally to the results of the different reduction potential of diesel fuel, methyl ester or untreated oils. The combination of regenerative fuel and catalyst shows good potential for reducing the emissions. Furthermore the use of regenerative fuels is a sustainable production of energy with an overall efficiency of almost 90%. Regenerative fuels based on vegetable oils and waste fat are a valuable form of energy and have some significant advantages in comparison to diesel fuel, like an almost closed carbon dioxide cycle, rapid biological decomposition and lower CO, HC and particle emissions. Regenerative fuels should also meet minimum standards discussed in the paper to avoid the risk of engine damage and to reduce emissions.     

Experimental analysis of alternative fuel impact on a new “torque-controlled” light-duty diesel engine for passenger cars

The present paper describes the results of an experimental study performed burning alternative fuels, different per quality and feedstock, in a modern diesel engine compliance the Euro 5 emission standards. Three alternative fuels were tested on the engine and compared with a reference fossil fuel in terms of combustion characteristics, fuel consumption, noise and emissions. The alternative fuels were two biodiesels (RME and SME) and a Fischer-Tropsh (GTL), while the reference fuel was an EU certification diesel fuel. The engine employed in the study was a light-duty diesel engine developed for passenger car and light truck application, and equipped with the new generation ECU able to drive the engine under “torque-controlled” mode by means of instrumented glow-plugs with pressure sensor. The experiments were carried out in a fully instrumented test bench fuelling the engine with the various fuels. The tests were done in a wide range of engine operation points for the complete characterization of the biodiesels performance in the NEDC cycle. Moreover, the trade-off NO_x-PM by EGR sweep in the three most critical test points for the engine emission performance was carried out for all fuels. The test methodology was selected carefully in order to evaluate the interaction between the fuel quality and the engine management strategy. The results put in evidence a strong interaction between the alternative fuel quality and the engine control mode highlighting the great benefits reachable by exploiting simultaneously the alternative fuel quality and the flexibility of the new engine management strategies.     

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.     

Effects of ethyl tert-butyl ether addition to diesel fuel on characteristics of combustion and exhaust emissions of diesel engines

The effects of ethyl tert-butyl ether (ETBE) addition to diesel fuel on the characteristics of combustion and exhaust emissions of a common rail direct injection diesel engine with high rates of cooled exhaust gas recirculation (EGR) were investigated. Test fuels were prepared by blending 0, 10, 20, 30 and 40 vol% ETBE to a commercial diesel fuel. Increasing ETBE fraction in the fuel helps to suppress the smoke emission increasing with EGR, but a too high fraction of ETBE leads to misfiring at higher EGR rates. While the combustion noise and NO_x emissions increase with increases in ETBE fraction at relatively low EGR rates, they can be suppressed to low levels by increasing EGR. Though there are no significant increases in THC and CO emissions due to ETBE addition to diesel fuel in a wide range of EGR rates, the ETBE blended fuel results in higher aldehyde emissions than the pure diesel fuel at relatively low EGR rates. With the 30% ETBE blended fuel, the operating load range of smokeless, ultra-low NO_x (<0.5 g/kWi h), and efficient diesel combustion with high rates of cooled EGR is extended to higher loads than with the pure diesel fuel.     

Assessment of biodiesel blending detection capability of the on-board diagnostic of the last generation automotive diesel engines

Results of a research project aimed at studying the capability to develop a method (economic and simple) for on-board biodiesel blending detection are described. The method is based on the direct measurement of the Indicated Mean Effective Pressure (IMEP).The study was carried out on a 2.0L four-cylinder “torque-controlled” Euro 5 diesel engine for passenger car (PC) application. This engine, equipped with instrumented glow plug for combustion closed-loop control, represents the state of the art of the diesel engine control technology.Two biodiesels were chosen for the experiments: a rapeseed methyl-ester (RME) and an aged RME, while the conventional diesel fuel was an European (EU) certification diesel fuel.Results indicate generally a good response in blending detection of the method. However, in order to attain an acceptable accuracy, a pre-calibration appears necessary.     

Experimental study on diesel engine nitrogen oxide reduction running with jojoba methyl ester by exhaust gas recirculation

Jojoba methyl ester (JME) has been used as a renewable fuel in numerous studies evaluating its potential use in diesel engines. These studies showed that this fuel is a very good gas oil substitute but an increase in the nitrogenous oxides emissions was observed at all operating conditions. The aim of this study mainly was to quantify the efficiency of exhaust gas recirculation (EGR) when using JME fuel in a fully instrumented, two-cylinder, naturally aspirated, four-stroke direct injection diesel engine. The tests were made in two sections. Firstly, the measured performance and exhaust emissions of the diesel engine operating with diesel fuel and JME are determined and compared. Secondly, tests were performed at two speeds and loads to investigate the EGR effect on engine performance and exhaust emissions including nitrogenous oxides (NO_x), carbon monoxide (CO), unburned hydrocarbons (HC) and exhaust gas temperatures. Also, effect of cooled EGR with high ratio at full load on engine performance and emissions was examined. The results showed that EGR is an effective technique for reducing NO_x emissions with JME fuel especially in light duty diesel engines. A better trade-off between HC, CO and NO_x emissions can be attained within a limited EGR rate of 5-15% with very little economy penalty.     

Performance, emission and combustion evaluation of soapnut oil-diesel blends in a compression ignition engine

Soapnut (Sapindus mukorossi) oil, a nonedible straight vegetable oil was blended with petroleum diesel in various proportions to evaluate the performance and emission characteristics of a single cylinder direct injection constant speed diesel engine. Diesel and soapnut oil (10%, 20%, 30% and 40%) fuel blends were used to conduct short-term engine performance and emission tests at varying loads in terms of 25% load increments from no load to full loads. Tests were carried out for engine operation and engine performance parameters such as fuel consumption, brake thermal efficiency, and exhaust emissions (smoke, CO, UBHC, NO_x, and O₂) were recorded. Among the blends SNO 10 has shown a better performance with respect to BTE and BSEC. All blends have shown higher HC emissions after about 75% load. SNO 10 and SNO 20 showed lower CO emissions at full load. NO_x emission for all blends was lower and SNO 40 blend achieved a 35% reduction in NO_x emission. SNO 10% has an overall better performance with regards to both engine performance and emission characteristics.     

Experimental study of the performance and emission characteristics of diesel engine using direct and indirect injection systems and different fuels

An experimental study of the performance and emission characteristics of diesel engine using direct and indirect injection combustion systems are carried out on a same model of two diesel engines fuelled with diesel and the blend of diesel and Chinese pistache biodiesel. The results show that the NO_x emissions from the indirect injection combustion system (ICS) fuelled with diesel are reduced by around two thirds, compared to that from direct injection combustion system (DCS). Smoke emissions from the engine using ICS are all significantly lower than that of DCS, reduced by 70% for diesel; by 50-60% for the blend. The brake thermal efficiencies (BTEs) reduced by 8-10%, compared to that of DCS; the fuel consumptions increased by around 7-9%. It is also found that carbon monoxide (CO) emissions are reduced when the engine run at engine high power outputs, so are the hydrocarbon (HC) emissions from ICS at the peak power outputs. It is found that, when fuelled with the blend, the effects of ICS to the performance and emissions of diesel engine are very similar to that of running with diesel. For ICS engine fuelled with diesel and the blend fuel, the BSFCs for the blend are around 5% higher; the BTEs are around 2-4% lower; the reductions of NO_x from the blend fuel are 5.1-8.4% on average for the ICS; the reductions of smoke from the blend fuel are 26.8-31.7% on average for the ICS. CO emissions are around a half lower; and HC emissions are around one fifth lower, compared to that of fuelling with diesel. Comparing to that of DCS fuelled with diesel, using ICS fuelled with the blended fuel has much lower emissions. NO_x emissions decreased by 65.6% and 66.1%; smoke emissions decreased by 75.7% and 80.2%; CO emissions decreased by 55.8% and 46.0%; HC emissions decreased by 24.9% and 18.9%; with the BSFCs around 14.6-14.9% higher and the BTEs around 9.7-10.0% lower.     

Low temperature exhaust gas fuel reforming of diesel fuel

The application of exhaust gas assisted fuel reforming in diesel engines has been investigated. The process involves hydrogen generation by direct catalytic interaction of diesel fuel with engine exhaust gas. Using a laboratory reforming mini reactor incorporated in the exhaust system of a diesel engine, up to 16% hydrogen in the reactor product gas was achieved at a reactor inlet temperature of 290 °C. The results showed that such levels of hydrogen can be produced with appropriate control of the reaction parameters at temperatures typical of exhaust gas temperatures of diesel engines operating at part load without any requirement for external heat source or air and steam supply. The use of simulated reformed fuel was shown to be beneficial in terms of engine exhaust emissions and resulted in reduction of NO_X and smoke emissions.     

Regulated and unregulated emissions from a light-duty diesel engine with different sulfur content fuels

Five different sulfur content fuels were used on a light-duty diesel engine to study the effect of fuel sulfur on emissions. Four regulated emissions: smoke, nitrogen oxide (NO_x), unburned hydrocarbon (HC) and carbon monoxide (CO) emissions of the engine were investigated, as well as three unregulated emissions: formaldehyde (HCHO), acetaldehyde (MECHO) and sulfur dioxide (SO₂). The smoke emission decreases continuously and remarkably with the fuel sulfur content, and the fuel sulfur has more influence on smoke emission at lower engine load. The concentration of NO_x emissions did not change significantly with the different sulfur content fuels. As the fuel sulfur content decreases, the concentrations of HC and CO emissions have distinct reduction. The HCHO emission values are very low. The MECHO emission decreases with increasing engine load, and it continuously decreases with the fuel sulfur content and it could not be detected at higher engine load with 50 ppm sulfur fuel. The SO₂ emission increases continuously with the engine load, and obviously decreases with the fuel sulfur contents.     

Combustion and emissions of a DI diesel engine fuelled with diesel-oxygenate blends

Combustion and emissions of a DI diesel engine fuelled with diesel-oxygenate blends were investigated. The results show that there exist the different behaviors in the combustion between the diesel-diglyme blends and the other five diesel-oxygenate blends as the diglyme has the higher cetane number than that of diesel fuel while the other five oxygenates have the lower cetane number than that of diesel fuel. The smoke concentration decreases regardless of the types of oxygenate additives, and the smoke decreases with the increase of the oxygen mass fraction in the blends without increasing the NO_x and engine thermal efficiency. The reduction of smoke is strongly related to the oxygen-content of blends. CO and HC concentrations decrease with the increase of oxygen mass fraction in the blends. Unlike conventional diesel engines fueled with pure diesel fuel, engine operating on the diesel-oxygenate blends presents a flat NO_x/Smoke tradeoff curve versus oxygen mass fraction.