Al-Khwarizmi Engineering Journal Al-Khwarizmi Engineering Journal, Vol. 8, No. 1, PP 65 -75 (2012) Effect of Fuel Cetane Number on Multi-Cylinders Direct Injection Diesel Engine Performance and Exhaust Emissions Sabah Tarik Ahmed Miqdam Tariq Chaichan Department of Machines and Equipments Engineering /University of Technology (Received 25 April 2011; accepted 25 December 2011) Abstract Due to the energy crisis and the stringent environmental regulations, diesel engines are offering good hope for automotive vehicles. However, a lot of work is needed to reduce the diesel exhaust emissions and give the way for full utilization of the diesel fuel’s excellent characteristics. A kind of cetane number improver has been proposed and tested to be used with diesel fuel as ameans of reducing exhaust emissions. The addition of (2-ethylhexyl nitrate) was designed to raise fuel cetane number to three stages, 50, 52 and 55 compared to the used conventional diesel fuel whose CN was 48.5. The addition of CN improver results in the decrease brake specific fuel consumption by about 12.55%, and raise brake thermal efficiency to about 9%. Simultaneously, the emission characteristics of four fuels are determined in a diesel engine. At high loads, a little penalty on CO and HC emissions compared to baseline diesel fuel. NOx emissions of the higher CN fuels are decreased 6%, and CO of these fuels is reduced to about 30.7%. Engine noise reduced with increasing CN to about 10.95%. The results indicate the potential of diesel reformation for clean combustion in diesel engines. Key words: CN improver, performance, exhaust emissions, NOx, UBHC,CO, CO2, noise. 1. Introduction Diesel fuel comes in several different grades, depending upon its intended use. Like gasoline, diesel fuel is not a single substance, but a mixture of various petroleum-derived components, including paraffins, isoparaffins, napthenes, olefins and aromatic hydrocarbons, each with their own physical and chemical properties. Diesel fuel must satisfy a wide range of engine types, differing operating conditions and duty cycles, as well as variations in fuel system technology, engine temperatures and fuel system pressures. It must also be suitable for a variety of climates. The properties of each grade of diesel fuel must be balanced to provide satisfactory performance over an extremely wide range of circumstances [1 & 2]. Probably the most familiar diesel fuel property to end users and for service and repair professionals is ignition quality, as expressed by cetane number. The cetane number (CN) is a measure of the ignition quality of diesel fuel based on the ignition delay in an engine. Consumers often think the cetane number is similar to the octane number for gasoline, but that is not the case. Octane is a measure of a spark ignition engine fuel’s (gasoline) ability to resist engine knock. Diesel cetane ratings work in the opposite direction. The higher the cetane rating, the shorter the ignition delay and the better the ignition quality . Reaching desired cetane levels also limits the aromatic content of diesel fuel [3 & 4]. Similar studies, (Ullman, 1989 & Ullman, 1990) [5 & 6] conduced that the value of the fuel CN was the key to reduce HC and CO emissions. Both the CN and aromatics content of the fuel affected NOx emissions. NOx increased as the CN is decreased and as the aromatics content is decreased. However, they showed that there is no simple answer to how the fuel properties affect emissions because different engines used in the investigation did not show similar effects. Cowley, 1993 [7], also reported that the main controlling factor for emissions in diesel engines Sabah Tarik Ahmed Al-Khwarizmi Engineering Journal, Vol.8, No.1, PP 65-75 (2012) 66 is the cetane number of the fuel, although, depending on the engine type, the density of the fuel can also have some effects. Similar trends have been observed by Gabele, 1986 [8], when recording exhaust emissions from a diesel passenger car. The fuels tested were a “high quality” fuel (CN 46.8 and low aromatic content) and a “low quality” fuel (CN 32.0 and a high aromatic content). Their results showed a decrease of up to 40% in HC, CO and NO, when using the “high quality” diesel fuel [9]. Shell and Mercedes-Benz companies have joined efforts to investigate the effects of diesel fuel properties (density, distillation range, cetane number and aeronautics content) on exhaust emissions in an advanced European indirect injection (101) passenger car and a modem commercial vehicle direct injection (DI) engine [10]. Their results indicated that the CN and not the total aromatics content accounted for the variation in NOx emissions. By increasing the CN, the NOx emissions were reduced, particularly when raising CN from levels of 45 to 55. Above CN 55 the reductions became rather small [11 & 12]. Contradicting results were found by Rantanen, 1993 [13]. Emissions were measured from four turbocharged direct injection engines chosen as representative types of existing heavy duty engines. The cetane number was found not to be important in reducing NOx emissions [14 &15]. This work represents a part of a continuing research efforts carried out over years at the Machines & Equipments Engineering Deprt. - University of Technology to provide improved knowledge of the combustion phenomena in fuels of internal combustion engines in general and the diesel engines in particular. The focus in this article is on investigating the effects of improveng cetane number of diesel fuel, on the performance and emission characteristics of multi cylinder direct injection diesel engine under variable operating conditions. 2. Experimental setup Experimental apparatus of engine under study is direct injection (DI), water cooled four cylinders, in-line, natural aspirated Fiat diesel engine (Fig. 1), whose major specifications are shown in Table 1. The engine was coupled to a hydraulic dynamometer through which load was applied by increasing the torque. This dynamometer was calibrated at the Central Organization for Measurments and Quality Control-Baghdad. Fig. 1. Photo of the Test Internal Combustion Engine. Table 1, Tested Engine Specifications . Engine type 4cyl., 4-stroke Engine model TD 313 Diesel engine reg Combustion type DI, water cooled, natural aspirated Displacement 3.666 L Valve per cylinder Two Bore 100 mm Stroke 110 mm Compression ratio 17 Fuel injection pump Unit pump 26 mm diameter plunger Fuel injection nozzle Hole nozzle 10 nozzle holes Nozzle hole dia. (0.48mm) Spray angle= 160 o Nozzle opening pressure=40Mpa The Multigas model 4880 emissions analyzer was used to measure the concentration of nitrogen oxide (NOx), unburned total hydrocarbon UBHC, CO2 and CO. The analyzer detects the CO, CO2, HC, NOx, and O2 content. The gases are picked up from the engine exhaust pipe by means of a probe. They are separated from water they contain through a condensate separating filter, and then they are conveyed in the measuring cell. A ray of Sabah Tarik Ahmed Al-Khwarizmi Engineering Journal, Vol.8, No.1, PP 65-75 (2012) 67 infrared light (which is generated by the transmitter) is send through optical filters on to the measured elements. The gases which are contained in the measuring cell absorb the ray of light in different wave lengths; according to their concentration. The H2, N2 and O2 gases due to their molecular composition (they have the same number of atoms), do not absorb the emitted rays. This prevents from measuring their concentration through the infrared system. The CO, CO2, NOx and HC gases, because of their molecular composition, absorb the infrared rays at specific wavelengths (absorption spectrum). This analyzer was calibrated at the Ministry of Environment- Iraq. Overall sound pressure was measured by precision sound pressure level meter supplied with microphone type 4615, as shown in Fig. 2; the devise was calibrated by standard calibrator type pisto phone 4220. Fig. 2. Overall Sound Pressure Used in Tests. Four kinds of diesel fuel with different cetane numbers were selected for the study. The conventional Iraqi diesel fuel (CN=48.5) was taken as baseline diesel. A common cetane improving additive, 2-ethylhexyl nitrate (also known as iso-octyl nitrate) is used to improve diesel fuel ignitability in small concentrations. It is commonly produced by several different manufacturers; the exact product used in these tests was manufactured under the name HiTec 4103. The more formal chemical formula is C8H17NO3, with the basic structure an ethyl hexane molecule with one of the hydrogen atoms replaced with an NO3 nitrate radical. It was used to raise cetane number in three different rates (CN=50, 52 &55). Fuel properties and the constitutions for the four fuels were measued at Al-Najaf Refinary laboratory. These properties are recorded in Table 2. Table 2, Properties of Cetane Numbers for the Four Tested Fuels. Properties Fuel 1 (low CN) Fuel 2 (medium CN) Fuel 3 (high CN) Fuel 4 (ultra high CN) Cetane Number 48.5 50 52 55 Density (g/ml) 0.838 0.846 0.853 0.856 Lower heating value (MJ/kg) 42.36 42.87 42.44 43.18 H:C ratio 1.8 1.87 1.88 1.99 Alkalines (%) 72 80 89 96 Olifines (%) 2 1 2 2 Aromatics (%) 26 19 17 2 The following equations were used in calculating engine performance parameters [16]: 1- Brake power 𝑏𝑝 = 2𝜋∗𝑁∗𝑇 60∗1000 𝑘𝑊 …(1) 2- Brake mean effective pressure 𝑏𝑚𝑒𝑝 = 𝑏𝑝 × 2∗60 𝑉𝑠𝑛 ∗𝑁 𝑘𝑁/𝑚2 … (2) 3- Fuel mass flow rate 𝑚 𝑓 = 𝑣𝑓 ×10 −6 1000 × 𝜌𝑓 𝑡𝑖𝑚𝑒 𝑘𝑔 𝑠𝑒𝑐 … (3) 4- Air mass flow rate 𝑚 𝑎,𝑎𝑐𝑡 . = 12 𝑕𝑜∗0.85 3600 × 𝜌𝑎𝑖𝑟 𝑘𝑔 𝑠𝑒𝑐 … (4) 𝑚 𝑎𝑡𝑕𝑒𝑜 . = 𝑉𝑠.𝑛 × 𝑁 60∗2 × 𝜌𝑎𝑖𝑟 𝑘𝑔 𝑠𝑒𝑐 … (5) 5- Brake specific fuel consumpotion 𝑏𝑠𝑓𝑐 = 𝑚 𝑓 𝑏𝑝 × 3600 𝑘𝑔 𝑘𝑊 .𝑕𝑟 … (6) Sabah Tarik Ahmed Al-Khwarizmi Engineering Journal, Vol.8, No.1, PP 65-75 (2012) 68 6- Total fuel heat 𝑄𝑡 = 𝑚 𝑓 × 𝐿𝐶𝑉 𝑘𝑊 7- Brake thermal efficiency 𝜂𝑏𝑡𝑕. = 𝑏𝑝 𝑄𝑡 × 100 % …. (7) The fuel properties show that the conventional diesel fuel has low cetane number, compared to the other improved diesel fuels. In the experiment, the above four fuel blends with different cetane numbers proportions were operated on the engine, meanwhile combustion characteristics were measured and analyzed at the same brake mean effective pressure (bmep), and these parameters were compared with those of pure diesel combustion in order to clarify the effect of cetane number on engine performance and emissions. Before testing any other diesel fuel with a different CN, the fuel lines were purged and the fuel filters were changed. The fuel supply line was later connected to the tank and the next diesel to be tested was fueled to the system. The engine was then run for a sufficient period of time in order to ensure that the last amount of the previously used fuel which could possibly still remain in the system was consumed. Experimental errors and uncertainties The difference between measured and true values of quantity is known as an error. By assigning a value of that error, an uncertinity is defined. The uncertinities in each individual measurment lead to uncertainities in experiment [17]. In general, the uncertainty in the results is: 𝑒𝑅 = 𝜕𝑅 𝜕𝑉1 𝑒1 2 + 𝜕𝑅 𝜕𝑉2 𝑒2 2 + ⋯ + 𝜕𝑅 𝜕𝑉𝑛 𝑒𝑛 2 0.5 …. (8) Where: 𝑒𝑅 : Uncertainty in the results R : a given function of the independent variables V1, V2, …, Vn or R=R(V1, V2, …, Vn). ei : uncertainty interval in the nth variable. The partial derivative 𝜕𝑅 𝜕𝑉1 is a measure of the sensitvity of the result to a single variable. The summarized analysis of the experimental accuracy of the measuring properties for some selected measuring devices is shown in Table (3). From these values the experiments uncertainties can be calculated: 𝑒𝑅 = 0.045 2 + 0.07 2 + 0.95 2 + 0.98 2 + 1.24 2 + 0.7 2 + 0.022 2 0.5 = ∓1.974 …(9) Table 3 Experimental Accuracies. Measurements Accuracies in this study Temperatures 0.045 Air flow 0.07 Fuel flow 0.95 Engine speed 0.98 Engine tourque 1.24 Sound presure level 0.7 Emitted exhaust gases concentrations 0.022 3. Results and Discussion Cetane number requirements of an engine will vary depending on engine size, speed and load variations, starting conditions and atmospheric conditions. Since a diesel engine ignites the fuel without a spark, proper cetane levels are very important. The air/fuel mixture is ignited by the combination of compression and heating of the air due to compression. The fuel injected into the cylinder at the precise time ignition is desired to optimize performance, economy and emissions. Fig. 3 represents the effect of CN on brake specific fuel consumption (bsfc) for the four tested fuels. Increasing fuel CN reduces bsfc, although it is still high at low loads. Increasing fuel’s CN improves combustion and raises combustion chamber temperatures. Increasing combustion chamber temperatures gives low fuel delay period, and gives better ignition. Reducing the load reduces temperatures inside combustion chamber, and increases fuel delay period, resulting in bad combustion that needs more fuel to compensate the lost power. Sabah Tarik Ahmed Al-Khwarizmi Engineering Journal, Vol.8, No.1, PP 65-75 (2012) 69 Fig. 3. CN Effect on Bsfc for Variable Loads . Increasing CN improved brake thermal efficiency, as Fig. 4 represents. Brake thermal efficiency is a criterion of the useful used thermal power produced from fuel burning. Burning improvements cuases higher brake thermal efficiency. CN indicates the ability of fuel for self ignition, its inceaments reduce delay period and lead to better combustion. So increasing CN in this paper from 48.5 to 55 increased brake thermal efficiency by 9% and reduced bsfc by 12.55%. Fig. 4. CN Effect on Brake Thermal Efficiency for Variable Loads. Exhaust gas temperatures are increased by increasing load, while increasing CN reduces these temperatures, as shown in Fig. 5. Increasing load needs more fuel to be burned which rises exhaust temperatures. On the other hand, increasing CN improves delay period, making the burning process to be completed at top dead center, giving chance to expand exhaust gases to give maximum power to piston, and to be cooled at power stroke. Increasing CN (from baseline CN=48.5) gave reduction in exhaust temperatures by 1.2, 6.1 and 9.3% for CN 50, 52 and 55 respectively. Fig. 5. CN Effect on Exhaust Gas Temperatures for Variable Loads. Brake power (bp) increased with increasing engine speed, as Fig. 6 illustrates. Increasing CN increases bp also. Brake power increased by 1.1, 3.88 and 5.6% for CN 50, 52 and 55 respectively compared with baseline diesel fuel (CN=48.5). CN increment reduces bsfc for all engine speed range, as Fig. 7 represents. Increasing CN increases burning efficiency giving more power with less fuel, and these improvements grow with increasing CN. Reductions in bsfc were 2.7, 3.9 and 5.5% for CN 50, 52 and 55 compared with baseline diesel (CN= 48.5). Fig. 6. CN Effect on Brake Power for Variable Engine Speeds. 0.14 0.16 0.18 0.2 0.22 0.24 0.26 0 20 40 60 80 100 b sf c ( k g /k W h ) bmep (kN/m2) N=1500 rpm, CR=17:1, IT=38°BTDC Diesel (CN= 48.5) Diesel (CN= 50) Diesel (CN= 52) Diesel (CN= 55) 100 150 200 250 300 350 400 450 500 0 20 40 60 80 100 e x h a u st g a s te m p e r a tu r e s (° C ) bmep (kN/m2) N=1500 rpm, CR=17:1, IT=38° BTDC Diesel (CN= 48.5) Diesel (CN= 50) Diesel (CN= 52) Diesel (CN= 55) 24 25 26 27 28 29 30 1000 1500 2000 2500 3000 B r a k e p o w e r ( k W ) Engine speed (rpm) CR=17:1, IT=38° BTDC, 44 kN/m2 Diesel (CN= 48.5) Diesel (CN= 50) Diesel (CN= 52) Diesel (CN= 55) 24 25 26 27 28 29 30 31 32 33 34 0 20 40 60 80 100 b r a k e t h e r m a l e ff ii c ie n c y ( % ) bmep (kN/m2) N=1500 rpm, CR=17:1, IT=38° BTDC Diesel (CN= 48.5) Diesel (CN= 50) Diesel (CN= 52) Diesel (CN= 55) Sabah Tarik Ahmed Al-Khwarizmi Engineering Journal, Vol.8, No.1, PP 65-75 (2012) 70 Fig. 7. CN Effect on bsfc for Variable Engine Speeds. Raising CN reduces exhaust gas temperatures for all engine speed range, as Fig. 8 indicates. Raising fuel CN improves burning efficiency, in turn raising indicated thermal efficiency and reducing bsfc, so these improvements reflect on exhaust temperatures. The reductions were 2.4, 5.94 and 9.24% for CN 50, 52 and 55 respectively compared with baseline diesel. Given the operating conditions, it is easy to see why cetane level is important. In addition to improving fuel combustion, increasing cetane level also tends to reduce emissions of nitrogen oxides (NOx). These emissions tend to be more pronounced when working with lower cetane number fuels as Fig. 9 shows. The decrease in CN caused an increase in NO, because of the long ignition delay. Fig. 8. CN Effect on Exhaust Gas Temperatures for Variable Engine Speeds. Fig. 9. CN Effect on NOx Concentrations for Variable Loads. Fig.10 shows the variation of the CO concentration in exhaust gas with variable engine loads, when the engine was operated on commercial diesel fuel of 48.5 CN, and modified fuel of 50, 52 and 55 CN diesel fuels. Carbon monoxide is the primary intermediate product in the hydrocarbon oxidation. The presence of CO in lean fuel- air mixtures exhaust is an indication that some of the CO produced through the oxidation reactions could not be oxidized further to carbon dioxide. With very lean engine operation and small load within the partial motoring region, the CO concentrations recorded imply that they also partially originate from the incomplete combustion. These emissions are reduced with increasing CN in the fuel by 11.79, 31.2 and 56.34 for CN 50, 52 and 55 respectively compared with baseline diesel fuel (CN=48.5). Fig. 10. CN Effect on CO Concentrations for Variable Loads. 0.025 0.05 0.075 0.1 0.125 0.15 0.175 0.2 0 20 40 60 80 100 C O c o n c e n tr a ti o n s (% v o l. ) bmep (kN/m2) N=1500 rpm, CR=17:1, IT=38BTDC Diesel (CN= 48.5) Diesel (CN= 50) Diesel (CN= 52) Diesel (CN= 55) 0.14 0.16 0.18 0.2 0.22 0.24 0.26 1000 1500 2000 2500 3000 b sf c ( k g /k W h ) Engine speed (rpm) CR=17:1, IT= 38° BTDC, 44 kN/m2 Diesel (CN= 48.5) Diesel (CN= 50) Diesel (CN= 52) Diesel (CN= 55) 300 350 400 450 500 550 600 1000 1500 2000 2500 3000 E x h a u st g a s t e m p e r a tu r e s (° C ) Engine speed (rpm) CR=17:1, IT= 38° BTDC, 44 kN/m2 Diesel (CN=48.5) Diesel (CN=50) Diesel (CN=52) Diesel (CN=55) 0 100 200 300 400 500 600 700 800 0 50 100 N O x c o n c e n tr a ti o n s (p p m ) bmep (kN/m2) N=1500 rpm, CR=17:1, IT=38BTDC Diesel (CN= 48.5) Diesel (CN= 50) Diesel (CN= 52) Diesel (CN= 55) Sabah Tarik Ahmed Al-Khwarizmi Engineering Journal, Vol.8, No.1, PP 65-75 (2012) 71 The variations of un-burnt hydrocarbons (UBHC) concentration in the exhaust gases have a very similar trend to that observed for the CO concentrations, as Fig 11 indicates. The figure shows that at low loads a considerable fraction of the hydrocarbons representing significant quantities of fuel can pass through the engine cylinder partially burned or un-reacted. When the engine runs at very light loads, the poor atomization of the diesel fuel with increased ignition delay, large cyclic variations and low charge temperature, result in a very low gaseous fuel utilization. Fig. 11. CN Effect on UBHC Concentrations for Variable Loads. At higher loads, when the diesel concentration in the cylinder charge is high enough, the UBHC tend to reduce. Diesel fuel with CN= 55 improved the utilization of the fuel up to 20% compared with baseline diesel. Also, it reduced the UBHC concentration in the exhaust, as compared to the 48.5 CN fuel. The CN 50 fuel had a slightly adverse effect. Little differences were found at very light loads, as well as at full load. CO2 concentrations increased with increasing CN from 48.5 to 55, as Fig. 12 represents. The CO2 increments were due to reduction in CO and UBHC concentrations, which oxided totally demonstrated better burning. Engine noise reduced due to increasing CN, as shown Fig. 13. Burning improvements gave smooth movements for dynamic parts, and reduces vibration which reflects on reducing engine noise, while increasing load acts in opposite of CN effect and increases noise. From the figure it is apparent that the measured sound level is the summation of these two effects. The reductions were 3.9, 7 and 11.67% for CN 50, 52 and 55 respectively compared with baseline diesel. Fig. 12. CN Effect on CO2 Concentrations for Variable Loads. Fig. 13. CN Effect on Sound Level for Variable Loads. The cetane number of a diesel fuel is a measure of its readiness to ignite. Fuels with higher cetane numbers will burn more efficiently, by releasing lower levels of emissions and give better fuel economy than fuels with lower cetane numbers as well as lesser emissions As Fig. 14 reveals, NOx concentrations are reduced with increasing CN, and it is reduced also with increasing engine speed. Increasing engine speed increases turbulence inside combustion chamber, and reduces the available time for NOx formation. Similarly, increasing CN improves burning by reducing delay period, resulting in a complete burning which consumes all oxygen in the chamber, as a result reducing NOx concentrations. These concentrations are reduced by 2.1, 2.9 and 6% for CN 50, 52 and 55 0 10 20 30 40 50 60 70 80 0 20 40 60 80 100 H C c o n c e n tr a ti o n s (p p m ) bmep (kN/m2) N=1500 rpm, CR=17:1, IT=38° BTDC Diesel (CN= 48.5) Diesel (CN= 50) Diesel (CN= 52) Diesel (CN= 55) 0 2 4 6 8 10 12 14 0 20 40 60 80 100 C O 2 c o n c e n tr a ti o n s (% v o l. ) bmep (kN/m2) N=1500 rpm, CR=17:1, IT=38° BTDC Diesel (CN= 48.5) Diesel (CN= 50) Diesel (CN= 52) Diesel (CN= 55) 70 75 80 85 90 95 100 0 20 40 60 80 100 S o u n d ( d B ) bmep (kN/m2) N=1500 rpm, CR=17:1, IT=38° BTDC Diesel (CN= 48.5) Diesel (CN= 50) Diesel (CN= 52) Diesel (CN= 55) Sabah Tarik Ahmed Al-Khwarizmi Engineering Journal, Vol.8, No.1, PP 65-75 (2012) 72 respectively. It can be supposed that these reductions are not enough to reduce NOx to the wanted limits without using other techniques, like exhaust gas recirculation (EGR). Fig. 14. CN Effect on NOx Concentrations for Variable Engine Speeds . UBHC concentrations are reduced with increasing engine speeds from 1000 rpm to 2250, after this speed these concentration start to increase, as Fig 15 shows. Increasing CN impact is reducing UBHC emissions due to improvements in fuel combustion and burning. While increasing engine speed from medium to high speed increases the air fuel mixture turbulence, pushing some fuel to the piston crevice where its burning will be difficult, and it will appear as UBHC. Fig. 15. CN Effect on UBHC Concentrations for Variable Engine Speeds . CO concentrations behave as UBHC, as Fig. 16 represents. For the same reasons of UBHC reduction and increment, CO concentrations are reduced by 5.67, 15.5 and 30.7% for CN 50, 52 and 55 compared to baseline diesel. Increasing CN has large effect in reducing CO and UBHC; it also has some effect on NOx concentration reduction. Fig. 16. CN Effect on CO Concentrations for Variable Engine Speeds. CO2 concentrations are increased with increasing engine speed as Fig. 17 illustrates. It also increases with increasing CN. Increasing engine speed needs more fuel to be burnt; as a result higher CO2 concentrations will be exhausted. Increasing CN will improve burning and reduce UBHC and CO concentrations, which reflect on increasing CO2 concentrations. Fig. 17. CN Effect on CO2 Concentrations for Variable Engine Speeds. Engine noise rises at low speed and reduces at high speed, as Fig. 18 shows. It is also reduced with increasing CN. One of the main factors that are known to affect the combustion noise is the 200 220 240 260 280 300 320 340 360 380 400 1000 1500 2000 2500 3000 N O x c o n c e n tr a ti o n s (p p m ) Engine speed (rpm) CR=17:1, IT= 38° BTDC, 44 kN/m2 Diesel (CN= 48.5) Diesel (CN= 50) Diesel (CN= 52) Diesel (CN= 55) 15 20 25 30 35 40 1000 1500 2000 2500 3000 H C c o n c e n tr a ti o n s (p p m ) Engine speed (rpm) CR=17:1, IT= 38°BTDC, 44 kN/m2 Diesel (CN= 48.5) Diesel (CN= 50) Diesel (CN= 52) Diesel (CN= 55) 0.025 0.035 0.045 0.055 0.065 0.075 0.085 1000 1500 2000 2500 3000 C O c o n te n t (% v o l. ) Engine speed (rpm) CR=17:1, IT= 38° BTDC, 44 kN/m2 Diesel (CN= 48.5) Diesel (CN= 50) Diesel (CN= 52) Diesel (CN= 55) 0 2 4 6 8 10 12 14 1000 1500 2000 2500 3000 C O 2 c o n c e n ta r ti o n ( v o l% ) Engine speed (rpm) CR=17:1, IT=38º BTDC, 44 kN/m2 Diesel (CN= 48.5) Diesel (CN= 50) Diesel (CN= 52) Diesel (CN= 55) Sabah Tarik Ahmed Al-Khwarizmi Engineering Journal, Vol.8, No.1, PP 65-75 (2012) 73 pressure rise rate during combustion. It has also been proven that the maximum rate of pressure rise is directly proportional to the sound pressure level (SPL) in decibels observed in the main chamber of a diesel engine. However, this work proved that increasing CN reduces engine noise by 1.95, 7.8 and 10.95 for CN 50, 52 and 55 respectively compared to baseline diesel fuel. Fig. 18. CN Effect on Sound Level for Variable Engine Speeds. 4. Conclusions The effects of CN improver on performance, gas emissions and combustion characteristics of a four cylinders, direct injection compression ignition engine fuelled with several diesel fuels containing various proportions of CN improver have been investigated, and compared to Iraqi conventional diesel fuel (baseline fuel with CN=48.5). The main conclusions obtained are as follows: 1. Fuel cetane number strongly affects the ignition delay and combustion phasing of this single-injection premixed diesel combustion mode. Increasing cetane number results in a shorter ignition delay, which for a given injection timing results in earlier combustion phasing. 2. The bsfc reduced compared to the baseline diesel. The maximum reduction reached (at constant speed and variable engine loads) was for diesel fuel with CN=55. The reduction was 12.55% compared with baseline diesel fuel. While at constant load and variable engine speed the reduction reached was 5.5% for diesel fuel with CN=55. 3. The brake thermal efficiency improved remarkably with increasing CN. The maximum increament attained was 9% for diesel fuel with CN=55 compared with baseline fuel. 4. Increasing fuels cetane numbers reduces exhaust gas temperatures. The maximum reduction obtained was 9.24% for diesel fuel with CN=55 compared with baseline diesel (CN=48.5). 5. Brake power increased with increasing fuel cetane number. The maximum increament achieved was 5.6% for diesel fuel with CN=55 compared with baseline fuel. 6. NOx emissions decreased simultaneously when diesel engine fueled with higher CN diesel fuels. The maximum reduction attained was 6% for diesel fuel with CN=55 compared with baseline fuel. 7. CO emission decreased with the increase of CN rating. The maximum reduction attained was 30.7% for diesel fuel with CN=55 compared with baseline fuel. 8. HC emission reduced by increasing CN rating of the fuel. 9. Engine noise reduced remarkably with increasing CN. 10. CO2 emissions increased with increasing fuel CN. 11. The impacts of CN on emissions vary with engine operating conditions. At high load conditions, it has stronger effects on emissions. While at low loads, it has slight effects on emission reduction. With the increasing CN, NOx emissions decrease a little, while CO emissions and unburned HC emissions decrease at most operating conditions. All the results indicate the potential of CN for clean combustion in diesel engines. 12. The study demonstrates that limited increaments in CN (from CN=48.5 to CN=50) gives insignificant improvement of engine performance and exhaust emissions. Notation IT injection timing CN cetane number DI direct injection N engine speed (rpm) T engine tourqe Vsn swept volume °BTDC degree before top dead centre bmep brake mean effictive pressure BTE brake thermal efficiency 70 75 80 85 90 95 100 1000 1500 2000 2500 3000 S o u n d ( d B ) Engine speed (rpm) CR=17:1, IT=38ºBTDC, , 44 kN/m2 Diesel (CN= 48.5) Diesel (CN= 50) Diesel (CN= 52) Diesel (CN= 55) Sabah Tarik Ahmed Al-Khwarizmi Engineering Journal, Vol.8, No.1, PP 65-75 (2012) 74 CA crank angle CR compression ratio UBHC unburnt hydrocarbon CO carbon monoxide CO2 carbon dioxide NOx nitrogen oxides dB decibel LCV Lower calorific value 5. Referances [1] Quingley et al, 2009. A review of fuel and additive performance in the new CEC F-98- 08 DW10 Injector Fouling test, Fuels Colloquim Esslingen. [2] Gunea C D. 1997. 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(2012 )75 - 65، صفحة 1، العذد 8 هجلة الخىارزهً الهٌذسٍة الوجلذ احوذ صباح طارق 75 هتعذد األسطىاًاتهحرك دٌسل العادم لتأثٍر الرقن السٍتاًً للىقىد على أداء وهلىثات ري حقي هباشر صباح طارق أحوذ هقذام طارق جٍجاى انجبيؼخ انزكُٕنٕجٍخ / قغى ُْذعخ انًكبئٍ ٔانًؼذاد الخالصة ثغجت أصيخ انطبقخ ٔيحذداد انزهٕس انجٍئً انًزشذدح، رقذو يحشكبد انذٌضل أيم جٍذ نًحشكبد انًشكجبد، ٔثكم األحٕال يطهٕة انكثٍش يٍ انؼًم نزقهٍم .يهٕثبد انؼبدو نًحشك انذٌضل، ٔاػطبء فشصخ نالعزخذاو األيثم نًٕاصفبد احزشاق ٔقٕد انذٌضل نهؼًم ػهى سفغ (ْكغٍم- ثبًَ ٍَزشاد اثٍم)رى اعزخذو َٕع يٍ إَٔاع يحغُبد انشقى انغٍزبًَ يغ ٔقٕد دٌضل نزقهٍم يهٕثبد انؼبدو، ٔقذ رًذ إضبفخ إٌ إضبفخ يحغٍ انشقى انغٍزبًَ َزج . 48.5 يقبسَخ يغ انٕقٕد انزجبسي انًغزخذو يحهٍب راد انشقى انغٍزبًَ 55، ٔ 52 ،50انشقى انغٍزبًَ نثالس يشاحم ًْ .%9، ٔسفغ نهكفبءح انحشاسٌخ انًكجحٍخ ثحذٔد %12.5 ثحذٔد ػُّ رقهٍم نالعزٓالك انُٕػً انًكجحً نهٕقٕد ػُذ أحًبل يشرفؼخ يقبسَخ نٕقٕد انذٌضل COٔ UBHC كًب رى قٍبط انًهٕثبد انُبرجخ ألَٕاع انٕقٕد األسثؼخ فً َفظ انٕقذ، ٔقذ نٕحع اسرفبع رشاكٍض ٔاَخفض %. 30.7 ثحذٔدCO، كًب قهذ نٓزِ انًجًٕػخ رشاكٍض %6 قهٍال ألَٕاع انٕقٕد راد انشقى انغٍزبًَ األػهى ثحذٔد NOxاألعبعً، ٔقهذ رشاكٍض ثضٌبدح انشقى انغٍزبًَ نهٕقٕد، أظٓشد انُزبئج انحبجخ إنى رحغٍٍ َٕػٍخ ٔقٕد انذٌضل انًُزج نهٕصٕل إنى يحشكبد دٌضل % 10.95ضجٍج انًحشك ثحذٔد .راد احزشاق َظٍف