Joseph R. Asik

Lean Air-Fuel Ignition System Comparison in a Fast-Burn Engine

Ignition system variables investigated were: plug type, ignition energy, ignition power input, firing duration, and a plasma jet ignitor. Lean air-fuel ignition limits were determined for four different ignition system combinations. The ignition limit at a given A/F condition was determined of the peak cylinder pressure. The ignition limit of the long duration ignition system (40-60 crankangle degrees) used with a surface-air gap plug was found to have the greatest spark angle tolerance. The plasma jet ignition system had the leanest projected lean misfire limit. Adding capacitance to a conventional plug to enhance the initial discharge was found to increase the initial rate of burning, but had little effect on the ignition limit. All the high energy ignition systems had comparable ISFC values. The air-fuel ratio at which the minimum IFSC occurred, however, was observed to shift to a leaner operating condition as the burn rate of the mixture was enhanced by the ignition system.

Ignitability experiments in a fast burn, lean burn engine

This paper demonstrates the first successful use of factorial statistical analysis in quantifying the effect of ignition system parameters on lean operation of a fast burn single cylinder engine. Ignition parameters investigated include plug type, plug number, ignition system, plug location, and ground electrode orientation with respect to the mean swirl generated flow direction. System performance is quantified by analyzing the coefficient of variance of the peak cylinder pressure and the 0-10% mass fraction burn time for various parameter combinations. To confirm the results from the factorial analysis technique, data from spark angle sweeps at constant flowrates are presented for the basic system and for two promising candidates that were selected from the factorial experiments. These candidates, a multi-ground electrode plug and a surface-air gap plug combined with more ignition energy, are shown to improve engine operation at lean gas-to-fuel ratio. Finally, a simplified thermodynamic engine model is utilized to predict what specific fuel consumption (ISFC) is attainable with stable operation at lean gas-to-fuel ratio. The value measured at the MBT+1% ISFC level, using the surface-air gap plug and more ignition energy at about 22:1 gas-to-fuel ratio, is found to be within experimental error of the predicted value.

A/F ratio estimation and control based on induced engine roughness

2 versions of an engine air-to-fuel (A/F) ratio estimator were described and evaluated through transient engine testing. A four-parameter model was derived from steady-state identification and a ten-parameter model was derived from transient identification. Inputs to both estimators include a fundamental metric that relates the instantaneous change in engine speed to prescribed fuel injector pulse width modulation. Additional inputs include many of the standard engine state and control variables. The performance of the ten-parameter A/F model was found to be superior to the four-parameter model under cold engine testing. A closed-loop PID A/F ratio control system was described in which the A/F ratio estimator provided state feedback. Under limited testing conditions the ten-parameter estimator was shown to reduce open-loop A/F ratio excursions. This work demonstrates the feasibility of designing an A/F ratio estimator based on the response of engine speed to fuel pulse width modulation and incorporating that estimator in a closed loop A/F ratio feedback control system. This work opens up the possibility of including this type of A/F estimator into an A/F observer and of investigating alternate A/F estimator structures, such as those obtained from artificial neural networks.

The Ferroresonant Capacitor Discharge Ignition (FCDI) System: A Multiple Firing CD Ignition with Spark Discharge Sustaining Between Firings

This paper describes an experimental programmable ignition system based on a new principle of operation. The ignition system provides for electronically controlled changes in spark duration, spark current level, and restriking rate. The ignition system also combines a very fast risetime with a controlled duration. Extensive multicylinder engine dynamometer test data are presented which indicate that improved ignition can be of benefit at marginal engine operating points. /GMRL/