Controlling fuel and diluent gas flow for a diesel engine operating in the fuel rich low-temperature-combustion mode

Abstract

The flow of a diluent gas supplied to a motoring engine was controlled at a diluent to air mass flow ratios of 10%, 30%, 50%, and 70%. This arrangement was a significant set up for running the engine in the Low-Temperature Combustion mode. The engine used was a 436 cc Yanmar Diesel engine, driven at constant 2200 rpm by a 10 hp AC powered dynamometer. Intake air flow was measured by a model FMA-903-V Air Velocity Transducer by Omega Engineering, Inc., and the diluent gas flow was both measured and controlled by a model FMA-2613A Mass Flow Controller, also by Omega Engineering, Inc. Both were connected to a computer through a National Instruments USB-6211 data acquisition hub, and the signals from both were processed in real time through National Instruments' LabView 8.2 software. The diluent gas used was nitrogen. The flow controller was found to have reasonable flow precision but poor flow accuracy at many of the flow rates encountered during this experiment, with a minimum steady state error of 3.7% for a flow rate of 207.4 Standard Liters Per Minute (SLPM), the highest flow studied, and a maximum error of 97.4% at 53.8 SLPM, the lowest flow studied.

(cont.) The substantial error at low flow rates stems from the rated lower flow limit of the controller of 250 SLPM. A relation describing the amount of steady state error present was determined empirically, and either this equation or the implementation of an external PI controller can be used in the controlling LabView environment to decrease the steady state error.