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This study examines the novel use of a strong presence of radical ignition (RI) species to augment flame front propagation in a two-stroke spark ignition (SI) engine. Periphery mounted secondary chambers enable the generation of these RI species in one cycle for use in the next cycle. These chambers are outfitted to enable fuel-insertion and rapid heat addition. The new technology examined in the study employs the chemistry of homogeneous combustion radical ignition (HCRI) for the RI species enhancement of pre-mixed charge (PC) SI. The aim is to see if this chemistry can increase the lean burn threshold of this 2-stroke engine with natural gas (NG). The analysis uses experimental data together with a full chemical-kinetics simulation formulation that also accounts for thermo-chemical and hydro-dynamic exchanges that are both between the chambers and with the environment. The mechanism for the chemical kinetics consists of 97 chemical reactions involving 33 species.

A detailed examination is made of the effects of internally generated “radicals” on the chemical-kinetics mechanism for CNG (compressed natural gas) combustion in a direct-injection (DI) diesel engine operating under ultra-lean fuel conditions at normal diesel compression ratios. The primary generating site for these “radical” chemical species is a set of mini-chambers located within the cylinder head. Explored in this study is the potential for controlling the autoignition timing of the engine by altering the rates of this radical generation process via the temperature management of these chambers. The study suggests that the temperature management of these secondary chambers may help enable the control of the ignition timings in response to engine load changes.

This study numerically examines the effects of select “radical species” on the hypergolic combustion of methanol fuel in a direct-injection (DI) naturally aspirated diesel engine at reduced compression ratios. These select radicals are generated via a set of micro-chambers (Figure 1) strategically placed within the piston at a location adjacent to the combustion bowl. Investigated are the effects of these radical species on the chemical-kinetics of main chamber autoignition. Also studied is the subsequent interactive radical generation processes and radical frozen equilibrium in both the micro and main chambers. In this new four-stroke numerical simulation, two open systems continuously interact, passing energy and chemical species between one another (through connecting vents) and with the manifold (via valves), while attempting to equalize pressure differences. The fuel is injected in such a way that the methanol enters the cylinder in a super-critical gas state and remains gaseous.

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.

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.

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).