Search Results

This paper examines the use of radial ignition (RI) at much lower than normal diesel compression ratios (CR's) in a novel direct-injection (DI) diesel rotary-combustion engine (RCE). Unique to this engine are periphery mounted secondary radical generation chambers (mini-chambers) capable of controlling the rates of radical generation. For this preliminary study the engine is operated on hydrogen under conditions conducive to homogeneous combustion RI (HCRI). One goal at the lower CR's normally needed in rotary-engine operations (<10:1) is to see whether HCRI alone can substantially extend the lean burn region of this rotary diesel engine with hydrogen as fuel. The ultimate aim is to enable high-power density operations with both low NOx emissions and low heat rejection. With these ends in mind a detailed examination is made (via simulation) of the effects of internally generated “radicals” on the combustion chemical-kinetics of this engine.

This study explores the potential for ethanol use in the DI-HCRI (direct-injection homogeneous-combustion radical-ignition) diesel engine with its periphery-mounted secondary radical-generation chambers (mini-chambers). The aim of this simulation study is to determine whether HCRI alone can extend the lean burn region of this four-stroke ethanol engine to include low NOx operations at normal diesel compression ratios. The simulation employs a highly modified variant of an earlier single-phase full-kinetics formulation and a new chemical-kinetics mechanism with 57 species and 371 reactions. The fuel is injected in the liquid phase within both of the separate-but-connected open systems representing the main and mini chambers. Thus a droplet spray model is included in this full chemical-kinetics formulation to account for the vaporization and mixing of the liquid fuel in both chambers.

Numerical examination is made of the use of methane in a direct-injection (DI) radial-ignition (RI) diesel rotary-combustion engine (RCE) while operating under ultra-lean fuel conditions at low compression ratios (CR's). The simulated engine is operated with the help of five percent hydrogen as a pilot. Homogeneous combustion under such conditions is made possible by radical species produced in periphery-mounted secondary chambers. The bulk of the mass of the radical species generated by these chambers is used in the subsequent cycle to initiate and control main chamber autoignition. One goal is to see whether DI-RI alone can substantially extend the lean-burn region of this engine to enable low-heat rejection high-power density operations with low NOx emissions. A detailed examination is made of the effects of internally generated “radicals” on methane combustion chemistry in the RCE.

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.

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).

The aim of this work is to establish a means for operating a four-stroke direct injection (DI) homogeneous-combustion radical-ignition (HCRI) engine robustly on hydrogen with low NOx emissions. To this end the use of fuel-insertion control for the fuel entering the radical generating mini-chambers is studied in some detail. The study points to the possibility that, if the compression ratios (CR's) are kept within the normal (conventional) range for diesel operations and heat losses are reduced, over its entire operating regime the hydrogen IC engine may be made to run with only one ignition mode: namely RI (radical ignition). Details of the altered chemistry of radical ignition and OH driven radical generation are studied numerically using a newer chemical-kinetics mechanism within two separate but connected open systems representing the distinctive main-chamber and mini-chamber processes.

This work represents an extension of the homogeneous combustion radical ignition (HCRI) process to a two-stroke direct injection (DI) diesel engine operated at normal diesel compression ratios (CR's). As in four-stroke DI-HCRI diesel engine variants, this engine has periphery mounted secondary radical generation chambers (mini-chambers ) that enable control of the radical generation process. One goal of this study is to see whether the use of HCRI alone can extend the lean burn region of the two-stroke DI engine to enable low NOx operations with hydrogen at such CR's. To this end, a detailed examination is made of the effects of internally generated “radicals” on the chemical-kinetics of the two-stroke radical ignition (RI) diesel cycle. The starting point for this simulation is a modified variant of the well corroborated formulation used in the earlier hydrogen four-stroke studies.