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In the twenty-first century, exhaust emission control will remain a major technical challenge especially as additional pressures for fuel and energy conservation mount. To address these needs, a wide variety of engine and powertrain options must be considered. For many reasons, the piston engine will remain the predominant engine choice in the twenty-first century, especially for conventional and/or parallel hybrid drive trains. Emissions constraints favor the conventional port fuel-injected gasoline engine with 3-way exhaust catalyst, while energy conservation favors direct-injection gasoline and diesel engines. As a result of recent technological progress from a competitive European market, diesels, and most recently, direct-injection (DI) diesels now offer driveability and performance characteristics competitive with those of gasoline engines. In addition, DI diesels offer the highest fuel efficiency.

The concentrations of oxides of nitrogen (NOx = NO + NO2) in engine crankcases interest lubricant technologists because NOx reactions with fuel and lubricant components are partially responsible for engine deposits and oil deterioration. To provide information hitherto unavailable in the literature, concentrations of NOx and NO2 were measured in the crankcase gas of a multi-cylinder engine operated at a variety of steady-state conditions. The concentrations of NOx and NO2 measured in the crankcase gas followed the same trends with changes in engine operating variables as the concentrations of NOx and NO2 in the exhaust gas. Specifically, increasing intake manifold pressure, spark advance, and compression ratio, generally increased the concentrations of NOx and NO2. Increasing the percent exhaust gas recirculation, however, decreased NOx and NO2 concentrations.