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This paper presents a combined numerical and experimental investigation of the characteristics of spark discharge in a spark-ignition engine. The main objective of this work is to gain insights into the spark discharge process and early flame kernel development. Experiments were conducted in an inert medium within an optically accessible constant-volume combustion vessel. The cross-flow motion in the vessel was generated using a previously developed shrouded fan. Numerical modeling was based on an existing discharge model in the literature developed by Kim and Anderson. However, this model is applicable to a limited range of gas pressures and flow fields. Therefore, the original model was evaluated and improved to predict the behavior of spark discharge at pressurized conditions up to 45 bar and high-speed cross-flows up to 32 m/s. To accomplish this goal, a parametric study on the spark channel resistance was conducted.

Fuel lean combustion and exhaust gas dilution are known to increase the thermal efficiency and reduce NOx emissions. In this study, experiments are performed to understand the effect of equivalence ratio on flame kernel formation and flame propagation around the spark plug for different low turbulent velocities. A series of experiments are carried out for propane-air mixtures to simulate engine-like conditions. For these experiments, equivalence ratios of 0.7 and 0.9 are tested with 20 percent mass-based exhaust gas recirculation (EGR). Turbulence is generated by a shrouded fan design in the vicinity of J-spark plug. A closed loop feedback control system is used for the fan to generate a consistent flow field. The flow profile is characterized by using Particle Image Velocimetry (PIV) technique. High-speed Schlieren visualization is used for the spark formation and flame propagation.

The influence of spark plug orientation on early flame kernel development is investigated in an optically accessible gasoline direct injection homogeneous charged spark ignition engine. This investigation provides visual understanding and statistical characterization of how spark plug orientation impacts the early flame kernel and thus combustion phasing and engine performance. The projected images of flame kernel were captured through natural flame chemiluminescence with a high-speed camera at 10,000 frames per second, and the ignition secondary discharge voltage and current were measured with a 10 MHz DAQ system. The combustion metrics were determined using measurement from a piezo-electric in-cylinder pressure transducer and real-time engine combustion analyzer. Three spark plug orientations with two different electrode designs were studied. The captured images of the flame were processed to yield 2D and 1D probability distributions.

In order to extend the operability limit of the gasoline compression ignition (GCI) engine, as an avenue for low temperature combustion (LTC) regime, the effects of parametric variations of engine operating conditions on the performance of six-stroke GCI (6S-GCI) engine cycle are numerically investigated, using an in-house 3D CFD code coupled with high-fidelity physical sub-models along with the Chemkin library. The combustion and emissions were calculated using a skeletal chemical kinetics mechanism for a 14-component gasoline surrogate fuel. Authors’ previous study highlighted the effects of the variation of injection timing and split ratio on the overall performance of 6S-GCI engine and the unique mixing-controlled burning mode of the charge mixtures during the two additional strokes. As a continuing effort, the present study details the parametric studies of initial gas temperature, boost pressure, fuel injection pressure, compression ratio, and EGR ratio.

Past experimental studies conducted by the current authors on a 13 liter 16.7:1 compression ratio heavy-duty diesel engine have shown that diesel-Compressed Natural Gas (CNG) Reactivity Controlled Compression Ignition (RCCI) combustion targeting low NOx emissions becomes progressively difficult to control as the engine load is increased. This is mainly due to difficulty in controlling reactivity levels at higher loads. For the current study, CFD investigations were conducted in CONVERGE using the SAGE combustion solver with the application of the Rahimi mechanism. Studies were conducted at a load of 5 bar BMEP to validate the simulation results against RCCI experimental data. In the low load study, it was found that the Rahimi mechanism was not able to predict the RCCI combustion behavior for diesel injection timings advanced beyond 30 degCA bTDC. This poor prediction was found at multiple engine speed and load points.

Gasoline compression ignition (GCI) technology shows the potential to obtain high thermal efficiencies while maintaining low soot and NOx emissions in light-duty engine applications. Recent experimental studies and numerical simulations have indicated that high reactivity gasoline-like fuels can further enable the benefits of GCI combustion. However, there is limited empirical data in the literature studying the gasoline compression ignition process at relevant in-cylinder conditions, which are required for further optimizing combustion system designs. This study investigates the temporal and spatial evolution of the compression ignition process of various high reactivity gasoline fuels with research octane numbers (RON) of 71, 74 and 82, as well as a conventional RON 97 E10 gasoline fuel. A ten-hole prototype gasoline injector specifically designed for GCI applications capable of injection pressures up to 450 bar was used.

In this paper, a model-based linear estimator and a non-linear control law for an Fe-zeolite urea-selective catalytic reduction (SCR) catalyst for heavy duty diesel engine applications is presented. The novel aspect of this work is that the relevant species, NO, NO2 and NH3 are estimated and controlled independently. The ability to target NH3 slip is important not only to minimize urea consumption, but also to reduce this unregulated emission. Being able to discriminate between NO and NO2 is important for two reasons. First, recent Fe-zeolite catalyst studies suggest that NOx reduction is highly favored by the NO 2 based reactions. Second, NO2 is more toxic than NO to both the environment and human health. The estimator and control law are based on a 4-state model of the urea-SCR plant. A linearized version of the model is used for state estimation while the full nonlinear model is used for control design.

Because of domestic production from renewable sources and their clean burning nature, alcohols, especially ethanol, have seen growing use as a blending agent and replacement for basic hydrocarbons in gasoline. The increasing use of alcohol in fuels raises questions on the safety of these fuels under certain non-operational situations. Modern vehicles use evaporative emission control systems to minimize environmental emissions of fuel. These systems must be relatively leak-free to function properly and are self-diagnosed by the vehicle On-Board Diagnostic system. When service is required, the service leak testing procedures may involve forcing test gases into the “evap” system and also exposure of the fuel vapors normally contained in the system to atmosphere. Previous work has discussed the hazards involved when performing shop leak testing activities for vehicles fuelled with conventional hydrocarbon gasoline [1, 2].

Dual-fuel pilot ignited natural gas engines have several intrinsic advantages relative to spark ignited; mainly higher thermal efficiency and lower conversion costs. The major drawback is associated with light loads. This paper discusses objectives, approaches, methods and results of the development of strategies which overcome the drawbacks and enhance the advantages. Development of a pilot fuel injection system, having a delivery of only 1 mm3 at a duration of 0.6 ms, was described in a previous paper. This paper concentrates on the results of strategies to reduce unburned methane in the exhaust and to increase the substitution of gas at light loads through skip-fire, by-passing boost air and exhaust gas recirculation techniques. Engine tests proved that with these strategies, diesel fuel replacement of more than 95% over the entire engine operating map, including idle, can be achieved and current and anticipated future emission standards satisfied.

Homogeneous Charge Compression Ignition (HCCI) combustion offers high fuel efficiency and some emissions benefits. However, it is difficult to control and stabilize combustion over a significant operating range because the critical compression ratio and intake temperature at which HCCI combustion can be achieved vary with operating conditions such as speed and load as well as with fuel octane number. Replacing part of the base fuel with reformer gas, (which can be produced from the base hydrocarbon fuel), alters HCCI combustion characteristics in varying ways depending on the replacement fraction and the base fuel auto-ignition characteristics. Because fuel injection quantities and ratios can be altered on a cycle-by-cycle basis during operation, injecting a variable blend of reformer gas and base fuel offers a potential HCCI combustion control mechanism.

A previously developed CFD-based optimization tool is utilized to find optimal engine operating conditions with respect to fuel consumption and emissions. The optimization algorithm employed is based on the steepest descent method where an adaptive cost function is minimized along each line search using an effective backtracking strategy. The adaptive cost function is based on the penalty method, where the penalty coefficient is increased after every line search. The parameter space is normalized and, thus, the optimization occurs over the unit cube in higher-dimensional space. The application of this optimization tool is demonstrated for the Sulzer S20, a central-injection, non-road DI diesel engine. The optimization parameters are the start of injection of the two pulses of a split injection system, the duration of each pulse, the exhaust gas recirculation rate, the boost pressure and the compression ratio.

The combination of on-board diagnostics and evaporative emission control (EVAP) systems has led to a growing need to identify and repair leaks in automotive EVAP systems. The normal leakfinding method involves purging the system with a smoke fluid, usually air or nitrogen containing an oil aerosol and then looking for a visual indication of the leak. The purge flow used to distribute smoke through the system displaces substantial amounts of fuel vapor from the tank vapor space and can also raise the oxygen level inside the fuel system. If any ignition source is present, the formation of flammable mixtures both inside and outside the vehicle systems can lead to a flash fire hazard associated with leak finding procedures. Currently available fire statistics (such as NFPA) are not sufficiently detailed to attribute service shop fires to specific testing procedures.

An experimental and modeling study was conducted to study the passive regeneration of a catalyzed particulate filter (CPF) by the oxidation of particulate matter (PM) via thermal and Nitrogen dioxide/temperature-assisted means. Emissions data in the exhaust of a John Deere 6.8 liter, turbocharged and after-cooled engine with a low-pressure loop EGR and a diesel oxidation catalyst (DOC) - catalyzed particulate filter (CPF) in the exhaust system was measured and used for this study. A series of experiments was conducted to evaluate the performance of the DOC, CPF and DOC+CPF configurations at various engine speeds and loads.

Despite progressive implementation of stringent emission regulations, vehicle tailpipe emissions remain the major source of air pollution problems in most urban areas. To control and reduce tailpipe pollutants, it is critical to understand in-use emissions as a basis for any future emission controls. At present, emission factors are mainly studied by chassis dynamometer methods. However, concerns have been raised about the extent to which emissions produced by on-road vehicles can be predicted using emission factors developed based on standardized dynamometer test procedures. This paper describes an on-board, in-use vehicle emissions measurement system which measures tailpipe emission rates while the vehicle is in real service experiencing complex traffic conditions, driver behavior and weather.

With concerns continuing to grow with respect to global warming from greenhouse gases, further regulations are being examined, developed and are expected for the emission of CO2 as an automobile exhaust. Renewable alternate fuels offer the potential to significantly reduce the CO2 impact of transportation. Hydrogen as a spark - ignition (SI) engine fuel provides this potential for significant CO2 reduction when generated from renewable resources. In addition, hydrogen has advantageous combustion properties including a wide flammable mixture range which facilitates lean burning and high dilution, fast combustion energy release and zero CO2 emissions. However, the high burning rates and fast energy release can lead to excessive in-cylinder pressures and temperatures resulting in combustion knock and high NOx emissions at stoichiometric operation.

Although HCCI engines promise low NOx emissions with high efficiency, they suffer from a narrow operating range between knock and misfire because they lack a direct means of controlling combustion timing. A series of previous studies showed that reformer gas, (RG, defined as a mixture of light gases dominated by hydrogen and carbon monoxide), can be used to control combustion timing without changing mixture dilution, (λ or EGR) which control engine load. The effect of RG blending on combustion timing was found to be mainly related to the difference in auto-ignition characteristics between the RG and base fuel. The practical effectiveness of RG depends on local production using a fuel processor that consumes the same base fuel as the engine and efficiently produces high-hydrogen RG as a blending additive.

Steady-state particulate loading experiments were conducted on an advanced production catalyzed particulate filter (CPF), both with and without a diesel oxidation catalyst (DOC). A heavy-duty diesel engine was used for this study with the experiments conducted at 20, 40, 60 and 75 % of full load (1120 Nm) at rated speed (2100 rpm). The data obtained from these experiments were used and are necessary for calibrating the MTU 1-D 2-Layer CPF model. These experimental and modeling results were compared to previous research conducted at MTU that used the same engine but an earlier development version of the combination of DOC and CPF. The motivation for the comparison of the two systems was to determine whether the reformulated production catalysts performed as good or better than the early development catalysts. The results were compared to understand the filtration and oxidation differences between the two DOC+CPF and the CPF-only aftertreatment systems.

Model-based control strategies are important for meeting the dual objective of maximizing NOx reduction and minimizing NH3 slip in urea-SCR catalysts. To be implementable on the vehicle, the models should capture the essential behavior of the system, while not being computationally intensive. This paper discusses the adequacy of two different reduced order SCR catalyst models and compares their performance with a higher order model. The higher order model assumes that the catalyst has both diffusion and reaction kinetics, whereas the reduced order models contain only reaction kinetics. After describing each model, its parameter identification and model validation based on experiments on a Navistar I6 7.6L engine are presented. The adequacy of reduced order models is demonstrated by comparing the NO, NO2 and NH3 concentrations predicted by the models to their concentrations from the test data.

Natural gas is a challenging fuel for HCCI engines because its single-stage ignition and rapid combustion make it difficult to optimize combustion timing over a significant load range. This study investigates direct injection of a pilot quantity of high-cetane fuel near TDC as a range extension and combustion control mechanism for natural gas HCCI engines. The EGR and load range is studied in a supercharged natural gas HCCI engine equipped with external EGR, intake heating and a direct injection system for n-heptane pilot fuel. The operating range and emissions are of primary interest and are compared between both the baseline HCCI engine with variable intake temperature and the direct injected HCCI (DI-HCCI) engine with constant intake temperature. Test results show the EGR and load range at fixed intake temperature can be extended using pilot direct injection.

Accurate individual cylinder Air Fuel Ratio (AFR) feedback provide opportunities for improved engine performance and reduced emissions in spark ignition engines. One potential measurement for individual cylinder AFR is in-cylinder ionization measured by employing the spark plug as a sensor. A number of previous investigations have studied correlations of the ionization signal with AFR and shown promising results. However the studies have typically been limited to single cylinders under restricted operating conditions. This investigation analyzes and characterizes the ionization signals in correlation to individual AFR values obtained from wide-band electrochemical oxygen sensors located in the exhaust runners of each cylinder. Experimental studies for this research were conducted on a 2.0L inline 4 cylinder spark ignited engine with dual independent variable cam phasing and an intake charge motion control valve.