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Cooled exhaust gas recirculation (EGR) is widely used in diesel engines to control engine-out NOx (oxides of nitrogen) emissions. A portion of the exhaust gases is re-circulated into the intake manifold of the engine after cooling it through a heat exchanger. EGR cooler heat exchangers, however, tend to lose efficiency and have increased pressure drop as deposit forms on the heat exchanger surface due to transport of soot particles and condensing species to the cooler walls. In this study, condensation of water vapor and hydrocarbons at the exit of the EGR cooler was visualized using a fiberscope coupled to a camera equipped with a complementary metal oxide semiconductor (CMOS) color sensor. A multi-cylinder diesel engine was used to produce a range of engine-out hydrocarbon concentrations. Both surface and bulk gas condensation were observed with the visualization setup over a range of EGR cooler coolant temperatures.

The focus of this study is to validate the predictive capability of a recently developed physiology based thermal comfort modeling tool in a realistic thermal environment of a vehicle passenger compartment. Human subject test data for thermal sensation and comfort was obtained in a climatic wind tunnel for a cross-over vehicle in a relatively warm thermal environment including solar load. A CFD/thermal model that simulates the vehicle operating conditions in the tunnel, is used to provide the necessary inputs required by the stand-alone thermal comfort tool. Comparison of the local and the overall thermal sensation and comfort levels between the human subject test and the tool's predictions shows a reasonably good agreement. The next step is to use this modeling technique in designing and developing energy-efficient HVAC systems without compromising thermal comfort of the vehicle occupants.

This work reports a CFD study on a 2-stroke (2-S) opposed piston high speed direct injection (HSDI) Diesel engine. The engine main features (bore, stroke, port timings, et cetera) are defined in a previous stage of the project, while the current analysis is focused on the assembly made up of scavenge ports, manifold and cylinder. The first step of the study consists in the construction of a parametric mesh on a simplified geometry. Two geometric parameters and three different operating conditions are considered. A CFD-3D simulation by using a customized version of the KIVA-4 code is performed on a set of 243 different cases, sweeping all the most interesting combinations of geometric parameters and operating conditions. The post-processing of this huge amount of data allow us to define the most effective geometric configuration, named baseline.

A Machine Learning (ML) approach is presented to correlate in-cylinder images of early flame kernel development within a spark-ignited (SI) gasoline engine to early-, mid-, and late-stage flame propagation. The objective of this study was to train machine learning models to analyze the relevance of flame surface features on subsequent burn rates. Ultimately, an approach of this nature can be generalized to flame images from a variety of sources. The prediction of combustion phasing was formulated as a regression problem to train predictive models to supplement observations of early flame kernel growth. High-speed images were captured from an optically accessible SI engine for 357 cycles under pre-mixed operation. A subset of these images was used to train three models: a linear regression model, a deep Convolutional Neural Network (CNN) based on the InceptionV3 architecture and a CNN built with assisted learning on the VGG19 architecture.

Thermal cabin comfort is the largest consumer of battery energy second only to propulsion in Battery Electric Vehicles (BEV’s). Accurate prediction of thermal comfort in the vehicle cabin with fast turnaround times will allow engineers to study the impact of various thermal comfort technologies and develop energy efficient Heating, Ventilation and Air Conditioning (HVAC) systems. In this study a novel data-driven model based on physics-guided Sparse Identification of Nonlinear Dynamics (SINDy) method was developed to predict Equivalent Homogeneous Temperature (EHT), Mean Radiant Temperature (MRT) and cabin air temperature under transient conditions and drive cycles. EHT is a recognized measure of the total heat loss from the human body that can be used to characterize highly non-uniform thermal environments such as a vehicle cabin. The SINDy model was trained on drive cycle data from Climatic Wind Tunnel (CWT) for a representative Battery Electric Vehicle.

A new electronic sensor has been developed to measure the time-resolved concentration of carbonaceous particulate matter (PM) emitted in engine exhaust. The sensor is approximately the size of a standard automotive spark-plug or lambda sensor and can be mounted directly in the engine exhaust. It consists of a pair of closely spaced electrically isolated electrodes that protrude into the exhaust flow. One electrode is given a voltage bias of 1000 V while the other is the signal electrode. The sensor is capable of providing cycle-resolved feedback on the carbonaceous PM concentration in the exhaust to the engine control unit (ECU), thereby enabling real-time control of engine operating parameters to lower PM emissions. This paper reports the results of an experimental study of various parameters that affect the performance of the electronic sensor.

Sector mesh modeling is the dominant computational approach for combustion system design optimization. The aim of this work is to quantify the errors descending from the sector mesh approach through three geometric modeling approaches to an optical diesel engine. A full engine geometry mesh is created, including valves and intake and exhaust ports and runners, and a full-cycle flow simulation is performed until fired TDC. Next, an axisymmetric sector cylinder mesh is initialized with homogeneous bulk in-cylinder initial conditions initialized from the full-cycle simulation. Finally, a 360-degree azimuthal mesh of the cylinder is initialized with flow and thermodynamics fields at IVC mapped from the full engine geometry using a conservative interpolation approach. A study of the in-cylinder flow features until TDC showed that the geometric features on the cylinder head (valve tilt and protrusion into the combustion chamber, valve recesses) have a large impact on flow complexity.

Effects of six different fuels on low temperature premixed compression ignition (PCI) combustion were experimentally investigated in this paper with a light-duty HSDI engine. The PCI combustion concept reduces NOx and smoke emissions simultaneously by low temperature and premixed combustion, respectively. To achieve low temperature and premixed combustion, the ignition delay is prolonged and the injection duration is shortened. Six fuels were chosen to examine the influence of cetane number (CN) and other fuel properties on low temperature PCI combustion. The fuel selection also included a pure Gas- to-Liquid (GTL) fuel and a blend of base diesel and 20% soy based biodiesel (B20). Fuel effects were studied over a matrix of seven part load points in the low temperature combustion mode. The seven part load points were specified by engine speed (RPM) and brake mean effective pressure (BMEP).

The growing applications of Computer-Aided Engineering (CAE) tools have been motivated by the need to create more effective product development processes. Computational Fluid Dynamics (CFD), as one of the CAE tools, has enjoyed growing popularity for analysis of many airflow situations, including road vehicle aerodynamics. In many cases, these applications have been limited by the level of predictive accuracy that is possible with CFD codes today. In the present exercise, simplified representations of three vehicle models (1:12 scale) were chosen to assess the overall level of predictability of the GMTEC CFD code, using detailed measurements that were made in a scale-model wind tunnel. The CFD computations used two turbulence models (standard k-εand RNG k-ε) and were matched to the experimental geometry and test conditions.

In light- and medium-duty diesel engines, piston bowl shape influences thermal efficiency, either due to changes in wall heat loss or to changes in the heat release rate. The relative contributions of these two factors are not clearly described in the literature. In this work, two production piston bowls are adapted for use in a single cylinder research engine: a conventional, re-entrant piston, and a stepped-lip piston. An injection timing sweep is performed at constant load with each piston, and heat release analyses provide information about thermal efficiency, wall heat loss, and the degree of constant volume combustion. Zero-dimensional thermodynamic simulations provide further insight and support for the experimental results. The effect of bowl geometry on wall heat loss depends on injection timing, but changes in wall heat loss cannot explain changes in efficiency.

A pilot-main injection strategy is investigated for a part-load operating point in a single cylinder optical Diesel engine. As the energizing dwell between the pilot and main injections decreases below 200 μs, combustion noise reaches a minimum and a reduction of 3 dB is possible. This decrease in combustion noise is achieved without increased pollutant emissions. Injection schedules employed in the engine are analyzed with an injection analyzer to provide injection rates for each dwell tested. Two distinct injection events are observed even at the shortest dwell tested; rate shaping of the main injection occurs as the dwell is adjusted. High-speed elastic scattering imaging of liquid fuel is performed in the engine to examine initial liquid penetration rates.

NOx adsorber catalysts are leading candidates for improving NOx aftertreatment in diesel exhaust. The major challenge in the use of adsorbers that capture NOx in the form of nitrates is their susceptibility to sulfur poisoning. Sulfur, which is present in diesel fuel, adsorbs and accumulates as sulfate (SO4-2) at the same adsorption sites as NOx, and, since it is more stable than nitrates, inhibits the ability of the catalyst to adsorb NOx. It is found that high temperature (> about 650 °C) in the presence of a reducing gas is required to release sulfur rapidly from the catalyst. Since the peak temperatures of diesel engine exhaust are below 400 °C, additional heat is required to remove the sulfur. This work describes a reformate-assisted “sulfur purge” method, which employs heat generated inside the NOx trap catalyst by exothermic chemical reactions between the oxygen in diesel exhaust and injected reformate (H2 + CO).

Regulated emissions and fuel consumption are the main constraints affecting internal combustion engine (ICE) design. Over the years, many techniques have been used with the aim of meeting these limitations. In particular, exhaust gas recirculation (EGR) has proved to be an invaluable solution to reduce NOx emissions in Diesel engines, becoming a widely used technique in production engines. However, its application has a direct effect on fuel consumption due to both the changes in the in-cylinder processes, affecting indicated efficiency, and also on the air management. An analysis, based on the engine Global Energy Balance, is presented to thoroughly assess the behavior of a HSDI Diesel engine under variable EGR conditions at different operating points. The tests have been carried out keeping constant the conditions at the IVC and the combustion centering.

A methodology for measuring oil viscosity in an internal combustion engine has been developed that is based on measured values of oil pressure and oil temperature at a relatively low engine speed near idle. Engine oil pressure results from the resistance of the oil to flow under the pumping action of the oil pump. The resistance to flow, in turn, is a function of both the viscosity of the oil and the flow rate. At a constant oil flow rate, a higher oil viscosity will result in a higher oil pressure. Oil viscosity is an important factor in determining the ability of the oil to provide effective lubrication and, for example, can be used as an indicator of the need to change the oil. This report describes the operational principles of the methodology for determining engine oil viscosity and a proof of concept based on a simple vehicle test.

Spot, or distributed, cooling and heating is an energy efficient way of delivering comfort to an occupant in the car. This paper describes an approach to distributed cooling in the vehicle. A two passenger CFD model of an SUV cabin was developed to obtain the solar and convective thermal loads on the vehicle, characterize the interior thermal environment and accurately evaluate the fluid-thermal environment around the occupants. The present paper focuses on the design and CFD analysis of the energy efficient HVAC system with spot cooling. The CFD model was validated with wind tunnel data for its overall accuracy. A baseline system with conventional HVAC air was first analyzed at mid and high ambient conditions. The airflow and cooling delivered to the driver and the passenger was calculated. Subsequently, spot cooling was analyzed in conjunction with a much lower conventional HVAC airflow.

We have examined the influence of piston wetting on the size distribution and mass of particulate matter (PM) emissions in a SI engine using several different fuels. Piston wetting was isolated as a source of PM emissions by injecting known amounts of liquid fuel onto the piston top using an injector probe. The engine was run predominantly on propane with approximately 10% of the fuel injected as liquid onto the piston. The liquid fuels were chosen to examine the effects of fuel volatility and molecular structure on the PM emissions. A nephelometer was used to characterize the PM emissions. Mass measurements from the nephelometer were compared with gravimetric filter measurements, and particulate size measurements were compared with scanning electron microscope (SEM) photos of particulates captured on filters. The engine was run at 1500 rpm at the Ford world-wide mapping point with an overall equivalence ratio of 0.9.

The major challenge in diesel NOx aftertreatment systems using NOx adsorbers is their susceptibility to sulfur poisoning. A new computational model has been developed for the thermal management of NOx adsorber desulfation and describes the exothermic reaction mechanisms on the catalyst surface in the diesel NOx trap. Sulfur, which is present in diesel fuel, adsorbs as sulfates and accumulates at the same adsorption sites as NOx, therefore inhibiting the ability of the catalyst to adsorb NOx. Typically, a high surface temperature above 650 °C is required to release sulfur rapidly from the catalyst [1]. Since the peak temperatures of light-duty diesel engine exhaust are usually below 400 °C, additional heat is required to remove the sulfur. This report describes a new mathematical model that employs Navier-Stokes equations coupled with species transportation equations and exothermic chemical reactions.

Cooled exhaust gas recirculation (EGR) is widely used in diesel engines to control engine out NOx (oxides of nitrogen) emissions. A portion of the exhaust gases is re-circulated into the intake manifold of the engine after cooling it through a heat exchanger known as an EGR cooler. EGR cooler heat exchangers, however, tend to lose efficiency and have increased pressure drop as deposit forms on the heat exchanger surface due to transport of soot particles and condensing species to the cooler walls. In our previous work surface condensation of water vapor was shown to be successful in removing a significant portion of the accumulated deposit mass from various types of deposit layers typically encountered in EGR coolers. Significant removal of accumulated deposit mass was observed for “dry” soot only deposit layers, while little to no removal was observed for the deposit layers created at low coolant temperatures that consisted of both soot and condensed hydrocarbons (HC).

Engine-out soot emissions are the result of a complex balance between in-cylinder soot formation and oxidation. Soot is formed in the diffusion flame, just after the lift-off length (LOL). Size and mass of soot particles increase through the diffusion flame and finally they are partially oxidized at the flame front. Therefore, engine-out soot emissions depend on the amount of soot formed and oxidized inside the combustion chamber. There is a considerable amount of work in the literature on characterization of soot formation. However, there is a clear lack of published research related to the characterization of soot oxidation. Thus, the main objective of the current research is to provide more knowledge and insight into the soot oxidation processes. For this purpose, a combination of theoretical and experimental tools were used. In particular, in-cylinder optical thickness (KL) was quantified with an optoelectronic sensor that uses two-color pyrometry.

Diesel piston bowl geometry can affect turbulent mixing and therefore it impacts heat-release rates, thermal efficiency, and soot emissions. The focus of this work is on the effects of bowl geometry and injection timing on turbulent flow structure. This computational study compares engine behavior with two pistons representing competing approaches to combustion chamber design: a conventional, re-entrant piston bowl and a stepped-lip piston bowl. Three-dimensional computational fluid dynamics (CFD) simulations are performed for a part-load, conventional diesel combustion operating point with a pilot-main injection strategy under non-combusting conditions. Two injection timings are simulated based on experimental findings: an injection timing for which the stepped-lip piston enables significant efficiency and emissions benefits, and an injection timing with diminished benefits compared to the conventional, re-entrant piston.