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In-cylinder heat flux, cylinder pressure, and flame arrival and position data were obtained at air fuel ratios ranging from 11 - 16 at 3060 rpm and approximately 80% load. The engine used was a single cylinder, 5 hp, fixed timing, four stroke, overhead valve, air-cooled engine. Methods of mixture preparation include that produced with the stock carburetor, and with a system designed to provide the engine with a homogeneous mixture (HMS). Heat flux was measured using a thermopile device consisting of 300 thermocouple pairs. A thin film platinum RTD was used to measure the temperature at the thermopile and correct for sensitivity of the thermopile output to thermopile temperature. Flame arrival near the sensor was found through the analysis of an ion voltage signal from a probe located next to the heat sensor. An effort was made to identify and account for the variables which influence in-cylinder heat transfer.

The objective of this study was to observe and attempt to understand the effects of equivalence ratio and simulated exhaust gas recirculation (EGR) on the exhaust emissions and performance of a L-head single cylinder utility engine. In order to isolate these effects and limit the confounding influences caused by poor fuel mixture preparation and/or vaporization produced by the carburetor/intake port combination, the engine was operated on a premixed propane/air mixture. To simulate the effects of EGR, a homogeneous mixture of propane, air, and nitrogen was used. Engine measurements were obtained at the operating conditions specified by the California Air Resources Board (CARB) Raw Gas Method Test Procedure. Measurements included exhaust emissions levels of HC, CO, and NOx, and engine pressure data.

Cyclic variation is examined by: (1) conditional grouping and heat-release analysis to reveal different modes of combustion, (2) considering the order in which the burn modes occur to establish prior-cycle effects and (3) comparing the measured variation in IMEP with data generated by simple models. Results show that several burn modes may exist, particularly under fuel-lean conditions. Prior-cycle effects also become more obvious as the air-fuel ratio is increased. Finally, comparisons with data generated by simple models show that the nature of cyclic variation may range from completely stochastic to a superposition of a non-chaotic deterministic process on a stochastic process.

An in-cylinder optical sensor has been developed and tested for use in spark-ignition engine combustion analysis and control, This sensor measures the luminous emission in the near infrared region. Results of these tests show good correlation between the measured luminosity and traditional combustion parameters, such as location and magnitude of maximum cylinder pressure, and location and magnitude of maximum heat release. Engine performance indicators, such as the indicated mean effective pressure (IMEP), also can be determined accurately with the measured luminosity combined with other engine operating parameters, e.g. intake manifold pressure. In-cylinder air-fuel ratio can be determined with accuracy over an ensemble of 100 cycles.

In-cylinder heat flux and temperature measurements were obtained in an air-cooled four-stroke utility engine for a range of air-fuel ratios. For these measurements, the magnitude of the integrated heat flux peaked at the stoichiometric air-fuel ratio, with an approximately linear decrease on either side of stoichiometric. Advancing the spark generally increased the magnitude of the integrated heat flux. Evaluation of the Brake Specific Integrated Heat Flux (BSIHF) mitigated these trends, and, the effects of changes in timing were eliminated for some operating conditions Examination of the BSIHF from the compression and expansion stroke showed behavior mimicking the full cycle BSIHF. However, the fraction of the total flux contributed by this portion of the cycle varied greatly from approximately 98% of the total to approximately 75% of the total.

Measurements of the instantaneous heat flux at three positions on the cylinder head surface, and the steady-state cylinder head temperatures at four positions on the cylinder head have been obtained. Engine tests were performed for a range of air-fuel ratios including regimes rich of stoichiometric, stoichiometric, and lean of stoichiometric. In addition, ignition timing was advanced in increments from 22° BTDC to 40° BTDC. All tests were run with the throttle either fixed in the wide open position, or fixed in a position that produced 75% of the maximum power with the standard ignition timing and an air-fuel ratio of 13.5. This was done to ensure that changes in air mass flow rate were not influencing the results. In addition, all tests were performed with a fuel mixture preparation being provided by system designed to deliver a homogeneous premixed charge to the inlet port. This was done to ensure that mixture preparation issues were not confounding the results.