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The focus of the present study was to characterize Reactivity Controlled Compression Ignition (RCCI) using a single-fuel approach of gasoline and gasoline mixed with a commercially available cetane improver on a multi-cylinder engine. RCCI was achieved by port-injecting a certification grade 96 research octane gasoline and direct-injecting the same gasoline mixed with various levels of a cetane improver, 2-ethylhexyl nitrate (EHN). The EHN volume percentages investigated in the direct-injected fuel were 10, 5, and 2.5%. The combustion phasing controllability and emissions of the different fueling combinations were characterized at 2300 rpm and 4.2 bar brake mean effective pressure over a variety of parametric investigations including direct injection timing, premixed gasoline percentage, and intake temperature. Comparisons were made to gasoline/diesel RCCI operation on the same engine platform at nominally the same operating condition.

An experimental investigation of non-intrusive combustion sensing was performed using a tri-axial accelerometer mounted to the engine block of a small-bore high-speed 4-cylinder compression-ignition direct-injection (CIDI) engine. This study investigates potential techniques to extract combustion features from accelerometer signals to be used for cycle-to-cycle engine control. Selection of accelerometer location and vibration axis were performed by analyzing vibration signals for three different locations along the block for all three of the accelerometer axes. A magnitude squared coherence (MSC) statistical analysis was used to select the best location and axis. Based on previous work from the literature, the vibration signal filtering was optimized, and the filtered vibration signals were analyzed. It was found that the vibration signals correlate well with the second derivative of pressure during the initial stages of combustion.

Fuel spray atomization and breakup processes within a direct-injection spark-ignition (DISI) engine and outside the engine were modeled using a modified KIVA-3V code with improved spray models. The structures of the predicted sprays were qualitatively compared with planar images. The considered sprays were created by a prototype pressure-swirl injector and the planar images were obtained by laser sheet imaging in an optical DISI engine. In the out-of-engine case, the spray was injected into atmospheric air, and was modeled in a two dimensional bomb. In the engine case, the injection started from 270° ATDC, and full 3-D computations in the same engine were performed. In both cases, two liquid injection pressure conditions were applied, that is, 3.40 MPa and 6.12 MPa. The model gives good prediction of the tip penetration, and external spray shape, but the internal structure prediction has relatively lower accuracy, especially near the spray axis.

The University of Wisconsin-Madison Snowmobile Team has designed and constructed a clean, quiet, high performance snowmobile for entry in the 2008 Society of Automotive Engineers' Clean Snowmobile Challenge. Built on a 2003 cross-country touring chassis, this machine features a 750 cc fuel-injected four-stroke engine equipped with a fuel sensor which allows operation ranging from regular gasoline to an 85% blend of ethanol and gasoline (E85). The engine has been customized with a Mototron control system which allows for full engine optimization using a range of fuels from E00 to E85. Utilizing a heated oxygen sensor and a 3-way catalyst customized for this engine by W.C. Heraeus-GmbH, this sled reduces NOx, HC and CO emissions by up to 89% to an average specific mass of 0.484, 0.154, 4.94 g/kW-hr respectively. Finally, the Mototron system also allowed Wisconsin to extract another 4 kW from the Weber 750cc engine; producing 45 kW and 65 Nm of torque.

Simultaneous measurements of the radial and the tangential components of velocity are obtained in a high-speed, direct-injection diesel engine typical of automotive applications. Results are presented for engine operation with fuel injection, but without combustion, for three different swirl ratios and four injection pressures. With the mean and fluctuating velocities, the r-θ plane shear stress and the mean flow gradients are obtained. Longitudinal and transverse length scales are also estimated via Taylor's hypothesis. The flow is shown to be sufficiently homogeneous and stationary to obtain meaningful length scale estimates. Concurrently, the flow and injection processes are simulated with KIVA-3V employing a RNG k-ε turbulence model. The measured turbulent kinetic energy k, r-θ plane mean strain rates ( 〈Srθ〉, 〈Srr〉, and 〈Sθθ〉 ), deviatoric turbulent stresses , and the r-θ plane turbulence production terms are compared directly to the simulated results.

Cycle-to-cycle variation in combustion phasing and combustion rate cause knock to occur differently in every cycle. This is found to be true even if the end gas thermo-chemical time history is the same. Three cycles are shown that have matched combustion phasing, combustion rate, and time of knock onset, but have knock intensity that differs by a factor of six. Thus, the prediction of knock intensity must include a stochastic component. It is shown that there is a relationship between the maximum possible knock intensity and the unburned fuel energy at the time of knock onset. Further, for a small window of unburned energy at knock onset, the probability density function of knock intensity is self similar when scaled by the 95th percentile of the cumulative distribution, and log-normal in shape.

Dual-fuel reactivity controlled compression ignition (RCCI) engine experiments were conducted with port fuel injection of isooctane and direct injection of n-heptane. The experiments were conducted at a nominal load of 4.75 bar IMEPg, with low isooctane equivalence ratios. Two sets of experiments explored the effects of direct injection timing with single and double injections, and multi-dimensional CFD modeling was used to explore mixture preparation and timing effects. The findings were that if fuel-liner impingement is to be avoided, double injections provide a 40% reduction in CO and HC emissions, resulting in a 1% increase in thermal efficiency. The second engine experiment showed that there is a linear relationship between reactivity (PRF number) and intake temperature. It was also found that if the premixed fuel fraction is above a certain limit, the high-temperature heat release (HTHR) can be manipulated by changing the global PRF number of the in-cylinder fuel blend.

Large-eddy simulation (LES) is a useful approach for the simulation of turbulent flow and combustion processes in internal combustion engines. This study employs the ANSYS Forte CFD package and explores several key and fundamental components of LES, namely, the subgrid-scale (SGS) turbulence models, the numerical schemes used to discretize the transport equations, and the computational mesh. The SGS turbulence models considered include the classic Smagorinsky model and a dynamic structure model. Two numerical schemes for momentum convection, quasi-second-order upwind (QSOU) and central difference (CD), were evaluated. The effects of different computational mesh sizes controlled by both fixed mesh refinement and a solution-adaptive mesh-refinement approach were studied and compared. The LES models are evaluated and validated against several flow configurations that are critical to engine flows, in particular, to fuel injection processes.

This paper investigates the effect of E85 on load expansion and FTP modal point emissions indices under reactivity controlled compression ignition (RCCI) operation on a light-duty multi-cylinder diesel engine. A General Motors (GM) 1.9L four-cylinder diesel engine with the stock compression ratio of 17.5:1, common rail diesel injection system, high-pressure exhaust gas recirculation (EGR) system and variable geometry turbocharger was modified to allow for port fuel injection with gasoline or E85. Controlling the fuel reactivity in-cylinder by the adjustment of the ratio of premixed low-reactivity fuel (gasoline or E85) to direct injected high reactivity fuel (diesel fuel) has been shown to extend the operating range of high-efficiency clean combustion (HECC) compared to the use of a single fuel alone as in homogeneous charge compression ignition (HCCI) or premixed charge compression ignition (PCCI).

The three-dimensional CFD codes KIVA-II and KIVA-3 have been used together to study the effects of intake generated in-cylinder flow structure on fuel-air mixing and combustion in a direct injected (DI) Diesel engine. In order to more accurately account for the effect of intake flow on in-cylinder processes, the KIVA-II code has been modified to allow for the use of data from other CFD codes as initial conditions. Simulation of the intake and compression strokes in a heavy-duty four-stroke DI Diesel engine has been carried out using KIVA-3. Flow quantities and thermodynamic field information were then mapped into a computational grid in KIVA-II for use in the study of mixing and combustion. A laminar and turbulent timescale combustion model, as well as advanced spray models, including wave breakup atomization, dynamic drop drag, and spray-wall interaction has been used in KIVA-II.

DATA presented in this paper show temperature-time diagrams obtained from mufflers mounted on trucks which were traveling over their regular routes. Using these temperature data, specimens made of possible muffler materials were subjected to laboratory tests. A wide range of possible muffler materials and gas composition were covered in these tests. Results of the tests indicate that under long-run heavy-duty truck service, muffler failure occurs primarily because of high metal temperatures and that coated mild steel showed the most promise of longer muffler life.

Single droplet theory is used to simulate the behavior of fuel sprays in high-speed open-chamber diesels. A model for sprays in still air is presented which includes the air motion induced by the spray. Calculated paths and vaporization histories for droplets injected into swirling air are also presented. It is shown that the paths of vaporizing drops are closely approximated by solid sphere calculations. The effects of swirl speed, engine rpm, and squish air motion are also investigated.

The effects of numerical methodology in defining the initial conditions and simulating the compression stroke in D.I. diesel engine CFD computations are studied. Lumped and pointwise approaches were adopted in assigning the initial conditions at IVC. The lumped approach was coupled with a two-dimensional calculation of the compression stroke. The pointwise methodology was based on the results of an unsteady calculation of the intake stroke performed by using the STAR-CD code in the realistic engine and port geometry. Full engine and 60 deg. sector meshes were used in the compression stroke calculations in order to check the accuracy of the commonly applied axi-symmetric fluid dynamics assumption. Analysis of the evolution of the main fluid dynamics parameters revealed that local conditions at the time of injection strongly depend on the numerical procedure adopted.

To model sprays from pressure-swirl atomizers, the connection between the injector and the downstream spray must be considered. A new model for pressure-swirl atomizers is presented which assumes little knowledge of the internal details of the injector, but instead uses available observations of external spray characteristics. First, a correlation for the exit velocity at the injector exit is used to define the liquid film thickness. Next, the film must be modeled as it becomes a thin, liquid sheet and breaks up, forming ligaments and droplets. A linearized instability analysis of the breakup of a viscous, liquid sheet is used as part of the spray boundary condition. The spray angle is estimated from spray photographs and patternator data. A mass averaged spray angle is calculated from the patternator data and used in some of the calculations.

The long-term goal of this work is to develop a conceptual model for multiple injections of diesel jets. The current work contributes to that effort by performing a detailed modeling investigation into mechanisms that are predicted to control 1st and 2nd stage ignition in single-pulse diesel (n-dodecane) jets under different conditions. One condition produces a jet with negative ignition dwell that is dominated by mixing-controlled heat release, and the other, a jet with positive ignition dwell and dominated by premixed heat release. During 1st stage ignition, fuel is predicted to burn similarly under both conditions; far upstream, gases at the radial-edge of the jet, where gas temperatures are hotter, partially react and reactions continue as gases flow downstream. Once beyond the point of complete fuel evaporation, near-axis gases are no longer cooled by the evaporation process and 1st stage ignition transitions to 2nd stage ignition.

While Low Temperature Combustion (LTC) strategies such as Reactivity Controlled Compression Ignition (RCCI) exhibit high thermal efficiency and produce low NOx and soot emissions, low load operation is still a significant challenge due to high unburnt hydrocarbon (UHC) and carbon monoxide (CO) emissions, which occur as a result of poor combustion efficiencies at these operating points. Furthermore, the exhaust gas temperatures are insufficient to light-off the Diesel Oxidation Catalyst (DOC), thereby resulting in poor UHC and CO conversion efficiencies by the aftertreatment system. To achieve exhaust gas temperature values sufficient for DOC light-off, combustion can be appropriately phased by changing the ratio of gasoline to diesel in the cylinder, or by burning additional fuel injected during the expansion stroke through post-injection.

Premixed diesel combustion offers the potential of high thermal efficiency and low emissions, however, because the rapid rate of pressure rise and short combustion durations are often associated with low temperature combustion processes, noise is also an issue. The reduction of combustion noise is a technical matter that needs separate attention. Engine noise research has been conducted experimentally with a premixed diesel engine and techniques for engine noise simulation have been developed. The engine employed in the research here is a supercharged, single cylinder DI diesel research engine with a high pressure common rail fuel injection system. In the experiments, the engine was operated at 1600 rpm and 2000 rpm, the engine noise was sampled by two microphones, and the sampled engine noise was averaged and analyzed by an FFT sound analyzer.