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Research has shown that there are many factors that affect the long-term performance of nitrogen oxides (NOx) control systems used in diesel engine applications. However, if the NOx emissions can be accurately monitored, it might be possible to restore performance by making adjustments to the control systems. This paper presents results from a study that tested the durability of 25 NOx sensors exposed to heavy-duty diesel exhaust for 6,000 hours. The study, conducted by the Advanced Petroleum-Based Fuels - Diesel Emission Controls (APBF-DEC) project, tested the sensors at various locations in the exhaust stream.

A methodology for developing modal vehicle emissions and fuel consumption models is described. These models, in the form of look-up tables for fuel consumption and emissions as functions of vehicle speed and acceleration, are designed for simulations such as the Federal Highway Administration's TRAF-series of models. These traffic models are used to evaluate the impacts of roadway design on emissions and fuel consumption. Vehicles are tested on-road and on a chassis dynamometer to characterize the entire operating range of each vehicle. As a verification exercise the models were used to predict cycle emissions and fuel consumption, and the results were compared to certification-type tests on a different population of vehicles. Results of the verification exercise show that the developed models can generally predict cycle emissions and fuel consumption with error comparable to the variability of repeat dynamometer tests.

A methanol and a gasoline vehicle were each subjected to testing under severe short-trip driving conditions. Results show that the cool oil sump temperatures caused more fuel and water to collect in the oil of the methanol vehicle. Protective properties of both vehicles' oils degraded during short trips but rebounded somewhat during a subsequent long trip. Slightly warmer sump temperatures in longer short-trip driving resulted in no methanol dilution in the methanol vehicle's oil, and higher total volatiles contamination in the gasoline vehicle's oil. Freeway driving following the longer short trips promoted less rebound in the degraded oils' protective properties.

Tests were conducted using an ASTM Aviation Supercharge CFR engine to determine whether high levels of fuel-bound nitrogen lead to increased nitric oxide emissions in a supercharged engine. Fuel nitrogen levels were formulated by doping several different fuels with pyridine. The results of the testing on this particular engine indicate that the effects of fuel nitrogen on nitric oxide emissions were so small that they were masked by the uncertainties associated with the experimental procedures used. Comparisons with the results from other researchers suggest that the results of this study are probably associated with stratification of the fuel-air mixture. It is recommended that additional tests be conducted to investigate the effects of fuel-air mixing on fuel-nitrogen conversion.

An investigation has been made to determine the effects of the degree of fuel atomization on exhaust emissions, fuel consumption, lean limit, MBT spark timing, and cyclic variations in peak cylinder pressure. A single-cylinder engine was used to isolate the effects of atomization on combustion from the additional effects of maldistribution that would be present in a multicylinder engine. Three degrees of gasoline atomization were investigated, along with the case of a well-mixed charge of gaseous propane. The degrees of atomization investigated varied from “Good” (10-20 μm droplets) to “Bad” (400-700 μm droplets) to “Wall-Wetted” (400-700 μm droplets deposited on the intake-port walls). Results from this investigation show that the degree of atomization can have considerable effect on exhaust emissions, but little effect on fuel consumption.