Investigation of NOx Predictions from Biodiesel-fueled HCCI Engine Simulations Using a Reduced Kinetic Mechanism Univ. of Wisconsin - Madison

Format:

Conference/Event

Author/Creator:

Brakora, Brakora, author.

Contributor:

Reitz, Rolf D.

Conference Name:

SAE 2010 World Congress & Exhibition (2010-04-13 : Detroit, Michigan, United States)

Language:

English

Physical Description:

1 online resource

Place of Publication:

Warrendale, PA SAE International 2010

Summary:

A numerical study was performed to compare the formation ofnitric oxide (NO) and nitrogen dioxide (NO₂), collectively termedNOx, resulting from biodiesel and diesel combustion in an internalcombustion engine. It has been shown that biodiesel tends toincrease NOx compared to diesel, and to-date, there is no widelyaccepted explanation. Many factors can lead to increased NOxformation and it was of interest to determine if fuel chemistryplays a significant role. Therefore, in order to isolate the fuelchemistry from mixing processes typical in a compression ignitionengine, sprays were not considered in the presentinvestigation.The current study compares the NOx formation of surrogates forbiodiesel (as represented by methyl butanoate and n-heptane) anddiesel (n-heptane) under completely homogeneous conditions.Combustion of each fuel was simulated using the Senkin code forboth an adiabatic, constant volume reactor, and an adiabatic,single-zone HCCI engine model. The fuel chemistry is representedusing an updated version of a mechanism that combines reducedmechanisms for methyl butanoate and n-heptane. NOx chemistry ispredicted using a 19-step model that includes species and reactionsfor both thermal and prompt NOx.It was found that the biodiesel surrogate can cause a NOxincrease when compared to diesel surrogate, but the relativeincrease was small (3%) for most equivalence ratios. Thedifferences in initial temperatures required to match ignition timemake it difficult to definitively link the NOx increase to theoxygen in the fuel under these conditions. The largest NOx increase(26%) was seen at near-stoichiometric conditions. However, it wasfound that the fuel-bound oxygen in biodiesel did not increase NOxto the extent that the same amount of oxygen would create if itwere available in the surrounding air. While the presence of O₂ inthe biodiesel surrogate does slightly impact NOx formation, it doesnot appear to be a dominant factor for HCCI engines, where mixtureconditions are well below stoichiometric. In conventional dieselcombustion, where equivalence ratios are often abovestoichiometric, these results suggest that the fuel chemistry canplay a role in the observed NOx increase

Notes:

Vendor supplied data

Publisher Number:

2010-01-0577

Access Restriction:

Restricted for use by site license