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Technical Paper

Radical Controlled Autoignition at Reduced Compression Ratios in a Hydrogen D.I. Diesel Engine With Piston Micro-Chambers

2004-06-08
2004-01-1846
This four-stroke engine study examines how micro-chamber generated “radicals” can facilitate the robust control of autoignition in direct-injection (D.I.) diesel engines. These internally produced radicals enable combustion under much lower than normal diesel compression ratios (CR's) and temperatures and make the chemical-kinetics control of autoignition timing a reality. In an attempt to better understand the mechanisms enabling radical based chemical control, the altered chemistry of radical ignition is studied numerically for the case of H2 combustion. Numerical simulation is based on a detailed mechanism involving as many as 19 species and 58 reactions. This H2 chemical-kinetics mechanism is simultaneously solved within two separate but connected open systems representing the distinctive main-chamber and micro-chamber processes (Figure 1).
Technical Paper

Frozen Equilibrium and EGR Effects on Radical-Initiated H2 Combustion Kinetics in Low-Compression D.I. Engines Using Pistons with Micro-Chambers

2003-05-19
2003-01-1788
Using hydrogen as a fuel, this chemical-kinetics study qualitatively examines the phenomenon of “frozen equilibrium” in Stratified Charge Radical Ignition (SCRI) engines with direct injection (DI) and exhaust gas recirculation (EGR). In such engines, this phenomenon is believed to preserve select highly reactive species formed in the side chambers (called micro-chambers) embedded inside the piston bowl so that these species can be carried-over to enhance autoignition in the next engine cycle. In turn this enhancement makes possible ignition and combustion at compression ratios that are markedly lower than those considered “standard” (for a given fuel), resulting in reduced emissions. Analysis is based on a detailed chemical-kinetics mechanism that includes NOx production and makes use of up to 19 species and 58 reactions.
Technical Paper

Flame Quenching in the Micro-Chamber Passages of I .C. Engines with Regular-Symmetric Sonex Piston Geometry

2001-11-01
2001-28-0002
Both physical experiments and detailed chemical kinetics studies establish that Sonex micro-chambers imbedded in the walls of the piston bowl of an I.C. engine generate highly reactive intermediate chemical species and radicals- which, when allowed to mix with the fresh charge of the next cycle in the main chamber, substantially alter the chemical kinetics of main chamber combustion. A much more stable overall combustion process is observed, requiring substantially leaner air-fuel ratios than normal, and with much lower ignition temperatures. The net result, without any efficiency penalty, is an engine with an “ultra-clean” exhaust and with a greater tolerance to a wider range of fuels. Crucial to this process is the quenching of the flame in the passages connecting the micro-chambers to the piston bowl. It is flame quenching which enables the incomplete combustion of the charge trapped in the micro-chamber cavities.
Technical Paper

NOx Reduction Kinetics Mechanisms and Radical-Induced Autoignition Potential of EGR in I.C. Engines Using Methanol and Hydrogen

2001-11-01
2001-28-0048
This numerical study examines the chemical-kinetics mechanism responsible for EGR NOx reduction in standard engines. Also, it investigates the feasibility of using EGR alone in hydrogen-air and methanol-air combustion to help generate and retain the same radicals previously found to be responsible for the inducement of the autoignition (in such mixtures) in IC engines with the SONEX Combustion System (SCS) piston micro-chamber. The analysis is based on a detailed chemical kinetics mechanism (for each fuel) that includes NOx production. The mechanism for H-air-NOx combustion makes use of 19 species and 58 reactions while the methanol-air-NOx mechanism is based on the use of 49 species and 227 reactions. It was earlier postulated that the combination of thermal control and charge dilution provided by the EGR produces an alteration in the combustion mechanisms (for both the hydrogen and methanol cases) that lowers peak cycle temperatures-thus greatly reducing the production of NOx.
Technical Paper

Methanol Combustion in Low Compression Ratio D.I. Engines Enabled by Sonex Piston Design

2001-03-05
2001-01-1197
Using methanol as a fuel, this study examines the chemical-kinetics mechanism responsible for the enhancement of combustion in I.C. engines due to intermediate and radical chemical species produced in micro-chambers of Sonex Combustion System (SCS) pistons. This homogeneous combustion enhancement was first shown experimentally (in 1991) to be capable of enabling an IC engine to operate stably and smoke free on methanol over an entire engine map while using a compression ratio of only 17:1 and without a spark or other assists. The distinction is made between thermally induced variants of homogeneous combustion: HCCI and ATAC; and intermediate species/radical induced homogeneous combustion: LAG and SCRl (Stratified Charge Radical Ignition).
Technical Paper

Development of a New Concept Piston for Alcohol Fuel Use in a Cl Engine

1996-05-01
961078
The feasibility of the Sonex. Combustion System (SCS) has been investigated for alcohol use in a single-cylinder, naturally aspirated DI engine. The SCS concept is to utilize active chemical species mated in specially designed small cavities in the piston bowl to enhance pre-ignition chemical reactions. With a prototype SCS piston, the CI engine ran stably from full load to 75% load on neat methanol and ethanol at a compression ratio of 17.5:1, without any ignition assist. At low load conditions, preheating of intake air was used. The idea of utilizing chemistry effects in the SCS design was proven to be feasible as a cetane-improving technology.
Technical Paper

A Preliminary Study of Chemically Enhanced Autoignition in an Internal Combustion Engine

1994-03-01
940758
Chemically enhanced autoignition in a spark-ignited engine with a special design of piston geometry has been observed experimentally, in which the engine would operate stably without a spark, once it is started by spark ignition. Under this operation mode, the engine provides lower pollutant emissions including NOx. In this process, the intermediate species left from the previous cycle play a key role in the low temperature autoignition. The objective of this study is to determine the effect of some important radical and intermediate species, such as HO2, OH, and H2O2, on autoignition by a numerical modeling approach using a detailed chemical kinetic mechanism. The fuel studied is hydrogen. The effect of added HO2, OH and H2O2 on the characteristics of the autoignition of H2-air mixture is investigated. Chemically enhanced autoignition of H2-air in an internal combustion engine is also simulated.
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