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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 H 2 combustion. Numerical simulation is based on a detailed mechanism involving as many as 19 species and 58 reactions. This H 2 chemical-kinetics mechanism is simultaneously solved within two separate but connected open systems representing the distinctive main-chamber and micro-chamber processes (Figure 1). During the combustion cycle these two open systems continuously interact, passing energy and chemical species between one another and the atmosphere while attempting to equalize pressure differences.

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 NO x production and makes use of up to 19 species and 58 reactions. Along with detailed versions of the momentum and energy equations, this mechanism is simultaneously solved within the two separate but interactively connected open systems representing the individual main chamber and micro-chamber combustion processes. Part of the aim of the present study is to identify several of the engine processes and dominant chemical-kinetics sub-mechanisms responsible for the much lower compression ratios and reduced NO, emissions in SCRI-DI engines with EGR.

Numerical simulation of flow, combustion phenomena and pollutants emission characteristics have been obtained on an homogeneous-charged internal combustion engine having conventional flat piston and five other bowl-in-piston geometries. The code employed here uses the time marching procedure and solves the governing partial differential equations of multi-component chemically reactive flow by finite difference method. The transient solution is marched out in a sequence of time steps. The results show that the piston geometry affects the local flame properties which subsequently influences the pollutants emission level. The numerical results provide a cost effective means of developing advanced internal combustion engine chamber geometry design that provides high efficiency and low pollution. It is expected that increased computational tools will be used in the future for enhancing our understanding of the detailed combustion process in internal combustion engines and all other energy conversion systems. Such detailed information is critical for the development of advanced methods for energy conservation and environmental pollution control.

This document presents the results of an engineering study to demonstrate the technology for converting small gasoline spark-ignited engines, to burn kerosene type fuels to power small generators (0.5 to 3.0 kw). Commercially available (plus those in the developmental stage), reciprocating, two-stroke, four stroke and rotary engines were evaluated for their conversion potential. Unique combustion systems were identified and trade-off studies conducted on engine type, combustion systems, and modification required to burn kerosene type fuels, with special emphasis given to minimizing life cycle cost. Recommendations for the most feasible system are given.

Comparison is made of the nonsteady combustion and flow processes predicted by the method of characteristics for time dependent compressible flow in a heat balanced engine with photographic records of combustion flow fields observed by high speed Fastex Schlieren and holographic interferometry. Pressure exchange and the accompanying mass transport are demonstrated analytically and observed optically. Qualitative agreement between the initial top dead center calculation and photographic evidence is seen. Schlieren and interferometer records give typical combustion flow field interactions through all strokes of an operating four stroke glass walled two dimensional engine. At least four models of time dependent combustion are identified over the entire power stroke and the influence of geometry on the control of combustion chamber pressure and temperature is discussed. (Author)

The heat balanced or combined cycle engine with time dependent combustion sustained by two chamber geometry is demonstrated experimentally. Evidence of time dependent heat addition is given where combustion creates a field of pressure waves sustained by pressure exchange between two chambers. The basic cycle and operating characteristics are reviewed and experimental results with CFR and glass-walled engines demonstrate the engine characteristic as compared to OTTO engines. Improvements in thermal efficiency over the OTTO engine in excess of 45 percent are demonstrated in some operating regimes. Considerable reduction in peak pressure and exhaust emission is also demonstrated.

An experimental and analytic analysis of water‐vapor condensation zones in moist‐air expansions is considered where the heat addition of condensation exceeds that for thermal choking. The transition from an unchoked to a choked flow is shown experimentally and described from the viewpoint of an analogous isentropic nozzle. Solution of the one‐dimensional equations of motion for a fully choked nozzle flow involving shock waves is given, and sonic point locations are verified experimentally. Special emphasis is given to the effect of heat addition and area variation on flow behavior in the region of sonic points. It is concluded that the onset of condensation in experiments involving shock waves can be used in testing theories of homogeneous nucleation.

Condensation of water vapor in a highly supersaturated state was studied with steady flow of moist air in supersonic nozzles of different temperature gradients. With measured centerline static pressures, known initial conditions, and known nozzle geometry, the equations of motion could be solved. From these results heat addition to the flow owing to condensation could be determined. By estimating latent heats, condensate mass fractions and condensation rates have been found. It was inferred that at temperatures from 200 to 220°K the condensate was ice. Classical steady‐state nucleation theories in conjunction with a droplet growth law were applied to solutions of the condensation integral equation. It was found that on this basis the onset of measurable condensation cannot be predicted from first principles. In a qualitative manner, however, the observations could be correlated with the theory. A contributing factor to the failure of nucleation theory is the lack of knowledge of material properties at the low temperatures in question. In conclusion, new work based on the findings of the conditions at the onset of condensation is suggested.