Experimental Study of Internal Injector Deposits In Internal Combustion Engines Using Renewable Fuels

Sammanfattning: The  strive  to  minimize  emissions  in  the  automotive  industry  keeps gaining momentum. Continuous improvement of engine designs and development of more efficient  fuel  systems  in  diesel  vehicles  is  a  solution to  be  applauded.  More importantly is the growing shift to use of renewable fuels in internal combustion engines.  With  countries  implementing  tighter regulations  on  emissions,  and markets  have  witnessed  a  rise  in  the  use of  biofuels.  Subsequently, the fuel quality varies from market to market. Blending  of  different  fuels  changes  the properties  of  fuel  as  solubility  of some  compounds  reduce.  Consequently,  soft particles  which  are precipitated  in  the  process  have  been  linked  to  deposit formation of internal diesel injector deposits (IDIDs). This project aims at investigating IDIDs and possible conditions that enhance their  formation  in  the  injector.  An injector test rig operating at actual engine pressures (>2000 bars) has been constructed for this purpose.  Test fuel for use in the rig is prepared at Scania by introducing soft particles into B10 fuel. Start of the test rig was performed by checking component functionality and pressure test. Due to leakage problem, a redesign of fuel collection cup was done. Evaluation of test fuel  was  carried  to  determine  the  suitability  for deposit  formation  in  the injector. Two screening tests were carried to investigate sticky deposit formation using the test fuel. Autoclave test was carried out at temperature of 150 0C over a period of up to four days. Frying pan test was performed to evaluate formation of deposits with increase in temperature between 90 0C to 230 0C. Analysis was carried out using SEM-EDX, GC-MS and FTIR instruments. The test fuel prepared at Scania for replication of deposits in the injector yielded positive results. Sticky deposits formed during the frying pan test evidenced by stretchy and sticky residue on the pan. FTIR analysis showed that the presence of metal carboxylate which is as a result of the metal ion soft particles. Autoclave tests showed formation of brown deposits on the vessel. SEM-EDX analysis of the brown deposits gave great insights on the morphology of the deposit contrasted to the structure of soft particles initially present in the test fuel. Soft particles are small and smeary with a regular shape while the deposits are large, irregular, agglomerated and rough in texture.  This is important in understanding the transformation mechanism of soft particles to deposits. A combination of calcium and sodium soft particles in the test fuel showed better ability to form deposits during   the   autoclave   test.   GC-MS   analysis   showed   huge   decrease   in   the concentration of soft particles in test fuel after autoclave tests compared to initial test fuel. In conclusion, the test fuel prepared works as expected and thus can be scaled up for running the injector test rig. Additionally, test fuel containing calcium and sodium soft particles have a higher probability to form deposits. Deposits were indeed proven to be metal carboxylates as expected.