Marc Baumgardner, PhD

Dual Fuel Combustion

**This project is an on-going collaboration with researchers at Colorado State University**

Autoignition of Liquid Hydrocarbon Droplets in Lean, High Pressure Natural Gas Mixtures Using a Rapid Compression Machine

Anthony J. Marchese (Colorado State University) and Marc E. Baumgardner (Gonzaga University)


Overview. The combustion of two fuels with disparate reactivity (i.e. dual fuel) in an internal combustion engine has been demonstrated as a means to increase fuel efficiency, reduce fuel costs and reduce pollutant formation in comparison to traditional diesel or spark ignited engines.  There is currently a major economic incentive to utilize natural gas in dual fuel applications and to maximize the substitution percentage of natural gas because of the historically low cost of natural gas per unit of energy relative to diesel fuel. However, since natural gas substitution schemes often utilize high compression ratio engines, the natural gas substitution percentage is limited by uncontrolled fast combustion or engine knock. To increase the natural gas substitution percentage, a greater understanding of the processes that lead to uncontrolled combustion rates in dual fuel engines is needed. Droplet ignition/combustion in a premixed fuel-air ambient under engine-like conditions (e.g. rapidly increasing temperature and pressure) represents an ideal environment to study dual fuel ignition phenomena because its geometric simplicity enables computations with full detailed chemistry with direct comparisons against optical diagnostics. Accordingly, the development of a system allowing the study of ignition and combustion of a liquid droplet in a lean premixed fuel-air environment in a rapid compression machine (RCM) represents a critical next step in exploring dual fuel combustion.

Intellectual Merit. Droplet evaporation and combustion has been studied for over 60 years and has proven to be an invaluable tool with which to examine a wide array of combustion applications. To date the bulk of research has consisted of examining droplets in O2/inert environments at near ambient temperatures and pressures. Studies conducted at elevated temperatures and pressures typically vary only one of these two parameters, and true engine-like conditions have only just begun to be examined. Additionally, true dual fuel combustion wherein the ambient is a lean mixture of fuel-air has not been substantially studied. The primary objectives of this study will be to demonstrate the ability to hold a droplet in fixed position under a lean ambient fuel-oxidizer environment subject to rapid temperature and pressure increases leading to evaporation and subsequent combustion and to optically examine said droplet throughout the entire process. Initially, due to the present interest in diesel-natural gas dual fuel engines, n-heptane fuel droplets will be combusted in lean methane/air environments. A secondary goal will be to develop an accurate chemical-kinetic mechanism capable of capturing the complex effects of diesel-natural gas dual fuel combustion for use in computational engine modeling. It is expected that the outcomes of this work will have substantial impact for enabling dual fuel combustion in current internal combustion engines and also many types of future combustion strategies.

To achieve these goals, the following specific tasks will be accomplished:

- Demonstrate the ability to ignite a stationary droplet in a stagnant flow field under rapidly increasing temperature and pressure in an RCM

- Examine optically the entire process of RCM compression leading to droplet evaporation, ignition of the premixed fuel/air vapor in the vicinity of the liquid droplet, ignition of the premixed natural gas/air mixture, propagation of a premixed natural gas/air flame away from the liquid droplet and non-premixed combustion of the liquid droplet.

- Quantify relevant combustion phenomena such as ignition conditions, ignition delays, flame spread rates, and minimum flammability limits of the lean ambient mixture as they relate to droplet ignition

- Develop a droplet ignition code capable of incorporating the relevant physics with sufficiently large chemical-kinetic mechanism so as to accurately describe the observed combustion

- Create an accurate reduced chemical mechanism capable of describing the initial dual fuel case of n-heptane droplets in lean methane/air environments

IMG_1447    hanging_drops1