Homogenous Charge Compression Ignition (HCCI) engines have the potential to achieve significant efficiency increases over spark-ignited engines, and significant emissions reductions compared to compression-ignited (Diesel) engines. Considerable research efforts are underway at major research centers worldwide to harness the advantages of this type of combustion and to overcome its obstacles. Here at the Combustion Analysis Laboratory, we are performing experimental research on the following aspects of HCCI:
- Control of combustion timing using fast thermal management and ion sensing
- The extension of higher load limits to increase power output of HCCI engines
- Combustion of wet ethanol fuels to achieve fuel savings during the fuel refining process
- The creation of a self-sufficient HCCI engine system capable of achieving the high intake air temperatures required for combustion of gasoline and alcohol fuels
- Testing various fuel blends to create a standard HCCI number (similar to Octane or Cetane ratings)
I am currently working on two research projects. The first consists of testing various fuels
in a Homogenous Compression Charge Ignition (HCCI) engine. The purpose of this research
is to determine characteristics for fuels that perform well in HCCI engines and spark ignited
(SI) engines.
The second consists of testing the feasibility of a novel high efficiency hydrogen-oxygen-argon
(H2-O2-Ar) engine that produces zero emissions. This research proposes operating
an H2-O2-Ar internal combustion (IC) engine that condenses the water produced by
combustion and recycles the Argon in a closed loop system. Basic engine theory predicts a
considerable increase in thermal efficiency (theoretically ~75%, and potential for ~50%
including heat transfer and friction losses) when using Ar because of its high specific heat
ratio (γ=1.67 compared to γ<1.4 for air).
In lean premixed (LP) gas turbine combustion, hot air from the compressor is mixed with natural gas as the air is ducted through swirl devices toward the combustion section where a sudden expansion of the flow path occurs. In the combustion section, it is widely believed that a turbulent flame propagates at a rate equal to the velocity of the stream in the combustion section. An alternate view is that hot premixed reactants enter the combustion section where there is recirculation causing the incoming reactants to "backmix" with hot products. The blending of hot products with incoming reactants leads to a new mixture at a temperature between reactants and products. At this new temperature, the mixture may rapidly autoignite. Thus, the apparent flame propagation is actually a zone of autoignition that is a consequence of mixing hot products with incoming reactants. This autoignition viewpoint is encouraged by the recognition of the flameless combustion in Homogeneous Charge Compression Ignition (HCCI). In HCCI engines, the precombustion temperatures and pressures are similar to the condition in the lean premixed gas turbine. The goal of this research is quantification of how much of the LP combustion can be attributed to autoignition as opposed to flame propagation. Our approach uses two fuels that have similar properties except for autoignition times. These fuels are chemical isomers of C2H6O, ethanol (CH3CH2OH) (EtOH) and dimethyl ether (CH3OCH3) (DME). These two fuels have similar laminar flame speeds, adiabatic flame temperatures, molecular masses, etc. However, the autoignition delay times of these fuels in air are different. Consequently, the use of these fuels affords the ability of investigating the role of autoignition in flame stabilization, while maintaining other stabilizing factors the same. Computational results show that as premixed reactant temperatures descend below 1000 K, the autoignition delay times of DME and EtOH diverge. Above 1000 K, the differences are increasingly indiscernible. Experimental research has been conducted in investigation of this hypothesis, and this research is ongoing.
