Alexander Knafl

Engine-in-the-Loop Testing for Evaluating Hybrid Propulsion Concepts and Transient Emissions - HMMWV Case Study

This paper describes a test cell setup for concurrent running of a real engine and a vehicle system simulation, and its use for evaluating engine performance when integrated with a conventional and a hybrid electric driveline/vehicle. This engine-in-the-loop (EIL) system uses fast instruments and emission analyzers to investigate how critical in-vehicle transients affect engine system response and transient emissions. Main enablers of the work include the highly dynamic AC electric dynamometer with the accompanying computerized control system and the computationally efficient simulation of the driveline/vehicle system. The latter is developed through systematic energy-based proper modeling that tailors the virtual model to capture critical powertrain transients while running in real time. Coupling the real engine with the virtual driveline/vehicle offers a chance to easily modify vehicle parameters, and even study two different powertrain configurations. In particular, the paper describes the engine-in-the-loop study of a V8, 6L engine coupled to a virtual 4x4 HighMobility Multipurpose Wheeled Vehicle (HMMWV). The results shed light on critical transients in a conventional powertrain and their effect on NOx and soot emissions. Next, the conventional HMMWV powertrain is replaced with a parallel hybrid electric configuration and two power management strategies are examined. Comparison of the conventional and hybrid propulsion options provides detailed insight into fuel economy – emissions tradeoffs at the vehicle level.

Comparison of Diesel Oxidation Catalyst Performance on an Engine and a Gas Flow Reactor

This paper analyzes and compares reactor and engine behavior of a diesel oxidation catalyst (DOC) in the presence of conventional diesel exhaust and low temperature premixed compression ignition (PCI) diesel exhaust. Surrogate exhaust mixtures of n-undecane (C11H24), ethene (C2H4), CO, O2, H2O, NO and N2 are defined for conventional and PCI combustion and used in the gas flow reactor tests. Both engine and reactor tests use a DOC containing platinum, palladium and a hydrocarbon storage component (zeolite). On both the engine and reactor, the composition of PCI exhaust increases light-off temperature relative to conventional combustion. However, while nominal conditions are similar, the catalyst behaves differently on the two experimental setups. The engine DOC shows higher initial apparent HC conversion efficiencies because the engine exhaust contains a higher fraction of trappable (i.e., high boiling point) HC. Engine DOC lightoff is delayed because in the tests performed, engineout CO was 11-30% higher than on the reactor, causing significant self-inhibition. The engine DOC also experiences ambient cooling, which further delays lightoff. Fully-lit HC conversion is lower on the engine because the reactor surrogate exhaust mixture does not include methane (CH4), which is unreactive at diesel light-off temperatures. Engine DOC heat loss and sample line HC desorption during post-DOC sampling also reduce fully-lit conversion on the engine.

In-cylinder reduction of PM and NOx emissions from diesel combustion with advanced injection strategies

The effect of advanced injection strategies, including pilot- and post-injections, on reducing pollutants from diesel combustion is investigated through a synergistic approach combining experiments and Computational Fluid Dynamics (CFD) simulations. It is shown experimentally that pilot injections have the potential to reduce NOx and particulate matter emissions simultaneously when the timing of the pilot is selected appropriately. To gain further understanding of the combustion and emissions formation mechanisms from multiple injection events, a CFD analysis is performed to model in-cylinder processes. Results show that benefits of pilot injection stem from improved fuel-air mixing and the reduction of the amount of diffusion combustion. Furthermore, CFD analysis demonstrates that post injection can accelerate the soot oxidation process if the injection timing and the amount of fuel are suitably selected, while simultaneously reducing NOx by reducing the amount of fuel in the main event and lowering peak combustion temperatures.