Single cylinder engine testing was carried out to clearly understand the test results of multi-cylinder engines reported by the Diesel WG in JCAP (Japan Clean Air Program) (1), (2), (3) and (4). In this tests, engine specifications such as fuel injection pressure, nozzle hole diameter, turbo-charging pressure, EGR rate, and fuel properties such as 1-, 2-, 3-ring aromatics content, n-,i-paraffins content, and T90 were parametrically changed and their influence on the emissions were studied. PM emission generally increased in each engine condition with increased aromatic contents and T90. In particular, multi ring aromatics brought about large increases in PM regardless of the engine conditions. The influence of fuel properties on NOx emission is smaller than the influence on PM emission. Some other fuels that have various side chain structures of 1-ring aromatics, normal paraffins only and various naphthene contents were also investigated.
Statistical analysis was also carried out to clarify determination factors on emissions. In the early stage of analysis, fuel density and 3-ring aromatics were found to be the determination factors for PM and NOx. The influence of fuel density, on the other hand, was considered to simply represent the influence of other fuel properties. This is because the physical effects of density should be minor under precisely controlled operation in this single cylinder engine testing. To interpret the influence of fuel density, a concept of residual density was introduced in sequential statistical analysis. The details of the residual density are explained in JCAP Combustion Analysis Working Group Report Part II (5). By introducing this “residual density” as an explaining variable instead of just “density,” aromatic contents and T90 appeared to be the determination factors of PM and NOx in most engine technical bases.