Isotopic Tracing of Fuel Components in Particulate Emissions from Diesel Engines using Accelerator Mass Spectrometry (AMS)
Accelerator mass spectrometry (AMS) is an isotope-ratio measurement technique developed in the late 1970s for tracing long-lived radioisotopes (e.g., {sup 14}C half life = 5760 y). The technique counts individual nuclei rather than waiting for their radioactive decay, allowing measurement of more than 100 low-level {sup 14}C samples per day (Vogel et al, 1995). The LLNL AMS system is shown in Fig.1. The contemporary quantity of {sup 14}C in living things ({sup 14}C/C = 1.2 x 10{sup -12} or 110 fmol {sup 14}C/ g C) is highly elevated compared to the quantity of {sup 14}C in petroleum-derived products. This isotopic elevation is sufficient to trace the fate of bio-derived fuel components in the emissions of an engine without the use of radioactive materials. If synthesis of a fuel component from biologically-derived source material is not feasible, another approach is to purchase {sup 14}C-labeled material (e.g., dibutyl maleate (DBM)) and dilute it with petroleum-derived material to yield a contemporary level of {sup 14}C. In each case, the virtual absence of {sup 14}C in petroleum based fuels gives a very low {sup 14}C background that makes this approach to tracing fuel components practical. Regulatory pressure to significantly reduce the particulate emissions from diesel engines is driving research into understanding mechanisms of soot formation. If mechanisms are understood, then combustion modeling can be used to evaluate possible changes in fuel formulation and suggest possible fuel components that can improve combustion and reduce PM emissions. The combustion paradigm assumes that large molecules break down into small components and then build up again during soot formation. AMS allows us to label specific fuel components, including oxygenates, trace the carbon atoms, and test this combustion modeling paradigm. Volatile and non-volatile organic fractions (VOF, NVOF) in the PM can be further separated. The VOF of the PM can be oxidized with catalysts in the exhaust stream to further decrease PM. The effectiveness of exhaust stream catalysts to oxidize products from tracer fuel components can be monitored through AMS measurement of carbon in PM. The objects of this report are: (1) Determine contribution of diesel fuel components and oxygenates to soot formation; (2) Separate volatile and non-volatile fractions of soot; (3) Test combustion paradigm that all carbon and oxygen in fuel is equal; and (4) Produce data to validate combustion modeling.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 15005712
- Report Number(s):
- UCRL-ID-144771; TRN: US0305610
- Resource Relation:
- Other Information: PBD: 2 Aug 2001
- Country of Publication:
- United States
- Language:
- English
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