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In order to evaluate the potential of several powertrain configurations, a well-to-wheel analysis is performed. Specifically, downsizing / supercharging and variable valve timing is examined and compared against other alternative vehicle concepts. In order to have a fair comparison, each powertrain configuration was added to a base vehicle, such that each vehicle had the same range, the same physical characteristics and similar performance. Upstream energy use and greenhouse gases were calculated with GREET 1.5a and the downstream energy use and greenhouse gases with ADVISOR 3.2. By downsizing / supercharging and adding variable valve timing, a spark ignition internal combustion engine can have comparable downstream overall efficiency, energy use, and greenhouse gas emissions, to a Diesel internal combustion engine.

Homogeneous Charge Compression Ignition (HCCI) is an emerging combustion technology due to its increased efficiency and decreased NOx emissions. One of the most challenging aspects of HCCI is the regulation of the combustion timing. Unlike conventional combustion modes there is no direct control over the start of combustion. Autoignition timing is a function of the temperature, pressure and composition of the mixture, so to adjust the combustion timing of HCCI changes have to be made to these. Both variable valve timing and variable fuel octane number are effective inputs to achieve cycle-to-cycle combustion control of HCCI combustion timing. The application of these control methods are investigated in this paper. A one-cylinder Ricardo engine is fitted with a 4-valve spark ignition cylinder head equipped with camshaft phasers. These phasers independently adjust both the intake and exhaust camshaft phasing.

A physics-based control-oriented model is developed to dynamically predict cycle-to-cycle combustion timing in transient fueling conditions for Homogeneous Charge Compression Ignition (HCCI) engines. The model simulates the engine cycle from the intake stroke to the exhaust stroke and includes the thermal coupling dynamics caused by the residual gases from one cycle to the next cycle. A residual gas model, a modified knock integral model, a fuel burn rate model, and thermodynamic models for the gas state in combustion and exhaust strokes are incorporated to simulate the engine cycle. The gas exchange process, generated work and completeness of combustion are predicted using semi-empirical correlations. The resulting model is parameterized for the combustion of Primary Reference Fuel (PRF) blends using 5703 simulations from a detailed thermo-kinetic model. Semi-empirical correlations in the model are parameterized using the experimental data obtained from a single-cylinder engine.

Experimental results are combined with a physical understanding of an amperometric NOx-O2 sensor to study the effect of three main operating parameters on the sensor behavior in non diffusion-rate-determining operating conditions. The sensor response to NOx concentration is examined over a range of sensor operating temperatures, reference cell potentials, and second sensing cell potentials. The results show that the sensor sensitivity increases gradually with the sensing cell voltage while the sensor output is almost linearly dependent on NOx concentration for cell voltages higher than ≈ 0.25 V. The results also reveal that reducing the reference cell potential from the typical cell potential (0.42 V) reduces the sensor cross-sensitivity to O2 particularly at high NOx concentrations (>600 [ppm]).

The effects of Variable Valve Timing (VVT) on Homogeneous Charge Compression Ignition (HCCI) engine energy distribution and waste heat recovery are investigated using a fully flexible Electromagnetic Variable Valve Timing (EVVT) system. The experiment is carried out in a single cylinder, 657 cc, port fuel injection engine fueled with n-heptane. Exergy analysis is performed to understand the relative contribution of different loss mechanisms in HCCI engines and how VVT changes these contributions. It is found that HCCI engine brake thermal efficiency, the Combined Heat and Power (CHP) power to heat ratio, the first and the second law efficiencies are improved with proper valve timing. Further analysis is performed by applying the first and second law of thermodynamics to compare HCCI energy and exergy distribution to Spark Ignition (SI) combustion using Primary Reference Fuel (PRF). HCCI demonstrates higher fuel efficiency and power to heat and energy loss ratios compared to SI.