Particle Emission Measurements in a SI CNG Engine using Oils with Controlled Ash Content 2019-01-0053
One of the inherent benefits of the gaseous fuel combustion, using a high methane content natural gas or biogas, is the clean combustion of the fuel. A single carbon atom in the fuel molecule results, to large extent, in particle-free combustion. This due to the high energy required of binding two or more carbon atoms together during the combustion process.
When scaling this process up and applying it in the internal combustion engine, the resulting emissions have not been observed to be as particle free as the theory indicates. One common practice has been to lower the engine oil ash content, as was done for diesel engines to reduce the particle emissions. For a gas engine, this has proven to be non-feasible as the piston lubrication becomes insufficient. The low particle emissions from the combustion of CNG allows for an investigation of particle contribution from engine oil ash content with only small particle contribution from the fuel itself.
The hypothesis for this study is that there is a relationship between the engine oil ash contents and the particulate emissions from a CNG engine. The investigation was conducted for several operating loads and engine speeds on a single cylinder engine. The single cylinder approach was chosen to reduce sources of engine oil intrusion in the combustion chamber. The results show particulate emissions in a spiking behavior, originating from the lubrication oil consumption past the piston rings. The particle numbers emission for the low ash content engine oil did not decrease but the size of the particles did. Variance in manifold pressure did not affect particle emissions. Mass flow through the engine proved to affect the particle size distribution as well as total particle number for all levels of oil ash content.
Ludvig Adlercreutz, Andreas Cronhjort, Ola Stenlaas
AVL MTC AB, KTH Royal Institute of Technology, Scania CV AB
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