THE AIM OF THIS PROJECT IS TO INVESTIGATE THE EFFECTIVENESS OF VARIOUS OCTANE BOOSTERS IN UNLEADED FUELS UNDER ENGINE CONDITIONS AT DIFFERENT SPEEDS AND LOADS. THE BOOSTER INFLUENCE ON THE FUEL CONSUMPTION AND EXHAUST EMISSION WILL ALSO BE EXAMINED.
The efficiency and output of an Otto engine can be improved by the use of the fuel components methanol, ethanol, methyl tert-buytl ether (MTBE) and tert-amyl methyl ether (TAME). Knock resistence of the blended fuels increased with an increasing amount of blending. It was about the same level for either component at equal rate of blending, indicating the octane number improving potential to be of the same order for all investigated components under the conditions of the investigations. For a given compression ratio this led to an increase in efficiency and output, if the knock limit of the basis fuel was located closer to top dead centre than the minimum spark advance for best torque. From higher blending rates advantages regarding efficiency can only be taken when the compression ratio is increased because of the higher octane requirement of Otto-engines with increased compression ratios.
Regarding exhaust emissions the use of the investigated oxygen containing fuel components caused an improvement in the case of specific carbon monoxide, nitrogen oxide and hydrocarbon emmissions for a given compression ratio and constant ignition timing, showing a slight advantage for the methanol blends. An increased amount of the blending components gave greater improvement. Running the engine at equal efficiency as for pure hydrocarbons also led to an improvement in nitrogen oxide emmissions. Fuel influence on nitrogen oxide emmissions was found out to be at a level of about 10%. This tendancy inversed when the advantage of the octane number improving potential of the blending components was used by advancing ignition timing. An improvement in emmissions of unburnt hydrocarbons could be obtained for each investigated fuel component. The improvement was a decreasing tendancy in the absolute amount of the hydrocarbon emmissions with increased blending rate. At the knock relevant region of the relative air fuel ratio of 1.0 no relevant influence of fuel composition on exhaust g as improvement, capable of fullfilling stringent exhaust standards could be detected. Each of the investigated components is capable of improving the fuel quality of unleaded fuels, when a considerable part of the fuel is substituted by either of the investigated components. Employing the components in engines of higher compression ratios than those in production at current times, leads to a better fuel economy assuming that a sufficient fuel quality of the basis pool is already obtained.
OCTANE BOOSTERS LIKE MTBE AND TAME ARE KNOWN TO BE EFFECTIVE. LITTLE IS KNOWN HOWEVER OF THEIR DETAILED OPERATING MECHANISM AND OF THEIR BEHAVIOUR AT DIFFERENT LOADS AND SPEEDS OF SERIES ENGINES AS WELL AS OF THE PROBLEM OF THE EXHAUST GASES TO WHICH THEY GIVE RISE. WHILE THE ELUCIDATION OF THEIR MECHANISM IS THE TASK OF ENSIC OF NANCY, LEHRSTUHL FUER KRAFT- UND ARBEITSMASCHINEN OF THE KAISERSLAUTERN UNIVERSITY WILL BE CONCERNED WITH THE REMAINING SUBJECTS.
TO A STANDARD FUEL, CONSISTING OF ISOOCTANE, N.HEPTANE AND TOLUENE THE PERCENTAGE OF WHICH WILL BE FIXED AFTER SOME PRELIMINARY EXPERIMENTS, THE FOLLOWING COMPONENTS WILL BE ADDED AT A 5%, 10% AND 20% LEVEL: MTBE, TAME, ETHANOL AND METHANOL. THE TEST ENGINE IS A 4-CYLINDER-OTTO-ENGINE ALLOWING SIMULTANEOUS PRESSURE INDICATIONS AT ALL CYLINDERS. THE COMPRESSION RATIO MAY BE ALTERED FROM 1/8 TO 1/15 BY CHANGING THE PISTONS.
THE STROKE VOLUME IS 1781 CC. AND THE RATIO STROKE/BORE 81,0/86,4. ITS PERFORMANCE IS 84 KW AND ITS SPEED 5500 RPM. THE ADJUSTMENT OF THE CORRECT AIR/FUEL RATIOS FOR EACH MIXTURE WILL BE POSSIBLE BY A BOSCH KE-JETRONIK FUEL INJECTOR. SEVERAL OPERATION POINTS AT FULL LOAD WILL BE CONSIDERED. THE KNOCKING BEHAVIOUR OF THE FUELS IS ESTIMATED FROM THE PRESSURE CONTOURS IN THE ENGINE CYLINDERS. KNOCKING COMBUSTION WILL BE PRODUCED BY SHIFTING THE IGNITION POINT UNTIL THE CYLINDER PRESSURE SHOWS THE CHARACTERISTIC HIGH-FREQUENCY OSCILLATIONS. THESE WILL BE COLLECTED BY A FAST DATA-ACQUISITION SYSTEM AND THEN STORED IN A COMPUTER. THE INTERPRETATION OF THE MEASURED VALUES WILL BE DONE USING VARIOUS CRITERIA: THE MAXIMUM AMPLITUDE, THE AVERAGE AMPLITUDE VALUE OR THE FREQUENCY OF THE OSCILLATIONS.
THE INFLUENCE OF THE ADDITIONS ON FUEL CONSUMPTION WILL ALSO BE CONSIDERED. BESIDES CO, NOX AND UNBURNT HYDROCARBONS, THE ALDEHYDE CONTENT OF THE EXHAUST GAS SHALL BE DETERMINED TO ASSESS THE EFFECTS OF THE ADDITIVES ON THE NOXIOUS COMPONENT OF THE EMISSIONS.