Effect of Volatiles on Soot Based Deposit Layers

The implementation of exhaust gas recirculation (EGR) coolers has recently been a widespread methodology for engine in-cylinder NOX reduction. A common problem with the use of EGR coolers is the tendency for a deposit, or fouling layer to form through thermophoresis. These deposit layers consist of soot and volatiles and reduce the effectiveness of heat exchangers at decreasing exhaust gas outlet temperatures, subsequently increasing engine out NOX emission. This paper presents results from a novel visualization rig that allows for the development of a deposit layer while providing optical and infrared access. A 24-hour, 379 micron thick deposit layer was developed and characterized with an optical microscope, an infrared camera, and a thermogravimetric analyzer. The in-situ thermal conductivity of the deposit layer was calculated to be 0.047 W/mK. Volatiles from the layer were then evaporated off and the layer reanalyzed. Results suggest that volatile bake-out can significantly alter the thermo-physical properties of the deposit layer and hypotheses are presented as to how.

A Research on Engine Phase and Speed Estimation Method Based on Cylinder Pressure Sensor

Cylinder pressure based combustion state control is a direction that has drawn much attention in the field of internal combustion engine control, especially in the field of diesel HCCI (Homogeneous Charge Compression Ignition) research. In-cylinder pressure sensors have the potential to diagnose or even replace many traditional sensors, including camshaft and crankshaft sensors. This paper did research on engine synchronization method based on in-cylinder pressure signal. The research was based on a 4-cylinder high pressure common rail diesel engine equipped with 4 PSG (Pressure Sensor Glow Plug) type piezo-resistance cylinder pressure sensors, intended for HCCI research. Through theoretical analysis and experimental proof, methods and models for cylinder identification, engine phase estimation and engine speed estimation are given and further verified by experiments. Results show that cylinder pressure sensor could be used to identify cylinder instead of cam shaft sensor. The models for engine phase and speed estimation have been proved to have precision of 3° crank angle and 4.6rpm, respectively. The precision of engine phase and speed estimation provides a possibility for the engine to run if the crankshaft sensor fails, but more researches have to be carried out with respect to crankshaft sensor replacement.

Development of a NOx Sensor Minimization Control Algorithm for Control of Gas Engines With NSCR

High exhaust emissions reduction efficiencies from a spark ignited (SI) internal combustion engine utilizing a Non Selective Catalyst Reduction (NSCR) catalyst system require complex fuel control strategies. The allowable equivalence ratio (Φ) operating range is very narrow where NSCR systems achieve high exhaust emission reduction efficiencies of multiple species. Current fuel control technologies utilizing lambda sensor feedback for natural gas spark ignited engines are reported to be unable to sustain these demands for extended operation periods and when transients are introduced. Lambda sensor accuracy is the critical issue with current fuel controllers. The goal of this project was to develop a minimization control algorithm utilizing an oxides of nitrogen (NOx) sensor installed downstream of the NSCR catalyst system for feedback air/fuel ratio control. Testing was performed on a 100kW rated natural gas Cummins-Onan generator set that was reconfigured to operate utilizing an electronic gas carburetor (EGC2) with lambda sensor feedback and high reduction efficiency NSCR catalyst system. The control algorithm was programmed utilizing a Labview interface that communicated with the electronic gas carburetor where the fuel trim adjustment was physically made. Improvement under steady state operation was observed. The system was also evaluated during load and fuel composition transients.

Cyclic Variability in Diesel/Gasoline Dual-Fuel Combustion on a Medium-Duty Diesel Engine

Most studies comparing diesel/gasoline dual-fuel operation and single-fuel diesel operation in diesel engines center on time-averaged results. It seems few studies discuss differences in cyclic variability. Motivated by this, the present study evaluates the cyclic variability of combustion in both dual-fuel and single-fuel operations of a diesel engine. Steady-state tests were done on a medium duty diesel engine with conventional direct injection timings of diesel fuel into the cylinder at one speed and three loads. In addition to single-fuel (diesel) operation, dual-fuel (gasoline and diesel) operation was studied at increasing levels of gasoline fraction. Gasoline fuel is introduced via a fuel injector at a single location prior to the intake manifold (and EGR mixing location). Crank-angle resolved data including in-cylinder pressure and heat release rate obtained for around 150 consecutive cycles are used to assess cyclic variability. The sources of cyclic variability, namely the factors causing cyclic variability or influencing its magnitude, especially those related to cylinder charge amount and mixture preparation, are analyzed. Fuel spray penetration and cyclic variability of cylinder charging, overall A/F ratio, and fuel injection timing, tend to increase cyclic variability of combustion in dual-fuel operation. On the other hand, fuel type and fuel spray droplet size tend to increase cyclic variability in single-fuel operation. The cyclic variability in dual-fuel operation in this study is more serious than that in single-fuel operation, in terms of magnitude, indicated by metrics chosen to quantify it. Most measures of cyclic variability increase consistently with increasing gasoline fraction. Variations of gasoline amount and possibly gasoline low temperature heat release cause higher combustion variation in dual-fuel operation primarily by affecting premixed burning. Statistical methods such as probability density function, autocorrelation coefficient, return map, and symbol sequence statistics methods are used to check determinism. In general, the parameters studied do not show strong determinism, which suggests other parameters must be identified to establish determinism or the system is inherently stochastic. Regardless, dominant sequences and optimal sequence lengths can be identified.

Model and Calibration of a Diesel Engine Air Path With an Asymmetric Twin Scroll Turbine

A control-oriented model and its associated tuning methodology is presented for the air path of a six cylinder 13 L diesel engine equipped with an asymmetric twin-scroll turbine, wastegate (WG), and exhaust gas recirculation (EGR). This model is validated against experimental engine data and shows good agreement. The small scroll of the asymmetric twin scroll turbine is fed by the exhaust of three cylinders via a split manifold that operates at higher pressure than the exhaust manifold feeding the larger turbine scroll. The asymmetric design with the high exhaust back pressure on three of the six cylinders gives the necessary EGR capability, with reduced pumping work, but leads to complex flow characteristics. The mean-value model describes the flows through the engine, the flow through the two turbine scrolls, the EGR flow, and the WG flow as they are defined, and defines the pressure of the manifolds they connect to. Using seven states that capture the dynamics of the pressure and composition in the manifolds and the speed of the turbo shaft, the model can be used for transient control, along with set point optimization for the EGR and WG flows for each speed and load condition. The relatively low order of the model makes it amenable to fast simulations, system analysis, and control design.

Optical Investigation of the Effects of Ethanol/Gasoline Blends on Spark-Assisted HCCI

Spark assist (SA) has been demonstrated to extend the operating limits of homogeneous charge compression ignition (HCCI) modes of engine operation. This experimental investigation focuses on the effects of 100% indolene and 70% indolene/30% ethanol blends on the ignition and combustion properties during SA HCCI operation. The spark assist effects are compared to baseline HCCI operation for each blend by varying spark timing at different fuel/air equivalence ratios ranging from ϕ = 0.4–0.5. High speed imaging is used to understand connections between spark initiated flame propagation and heat release rates. Ethanol generally improves engine performance with higher IMEPn and higher stability compared to 100% indolene. SA advances phasing within a range of ∼5 CAD at lower engine speeds (700 RPM) and ∼11 CAD at higher engine speeds (1200 RPM). SA does not affect heat release rates until immediately (within ∼5 CAD) prior to autoignition. Unlike previous SA HCCI studies of indolene fuel in the same engine, flames were not observed for all SA conditions.

Thermodynamic Considerations for Advanced, High Efficiency IC Engines

Thermodynamics is the key discipline for determining and quantifying the elements of advanced engine designs which lead to high efficiency. In spite of its importance, thermodynamics is often not given full consideration in understanding engine operation for high efficiency. By fully utilizing the first and second laws of thermodynamics, detailed understanding of the engine features that provide for high efficiency may be determined. Of all the possible features that contribute to high efficiency, the results of this study show that highly diluted engines with high compression ratios provide the greatest impact for high efficiencies. Other important improvements which increase the efficiency include reduced heat losses, optimal combustion phasing, reduced friction, and reduced combustion duration. Thermodynamic quantification of these concepts is provided. For one comparison, the brake thermal efficiency increased from about 34% for the conventional engine to about 48% for the engine with one set of the above features. One aspect that contributes to these improvements is the importance of the ratio of specific heats (“gamma”). In addition, these design features often result in low emissions due to the low combustion temperatures.

A Comparison of Valving Strategies Appropriate for Multi-Mode Combustion Within a Downsized Boosted Automotive Engine: Part B — Mid Load Operation Within the SACI Combustion Regime

Spark Assisted Compression Ignition (SACI) is a combustion mode that may offer significant efficiency improvements compared to conventional spark-ignited combustion systems. Unfortunately, SACI is constrained to a relatively narrow range of dilution levels and top dead center temperatures. Both positive valve overlap (PVO) and negative valve overlap (NVO) strategies may be utilized to attain these conditions at low and intermediate engine loads. The current work compares 1D thermodynamic simulations of PVO valving strategies and a baseline NVO strategy in a downsized boosted automotive engine with variable valve timing capability. As future downsized boosted engines may employ multiple combustion modes, the goal of this work is the definition of valving strategies appropriate for SACI combustion at low to moderate loads and SI combustion at moderate to high loads for an engine with fixed camshaft profiles. PVO durations, valve opening timings and peak lifts are investigated at low to moderate loads and are compared to a baseline NVO configuration in order to assess valving strategies appropriate for multi-mode combustion operation. A valvetrain kinematic model is used to translate the desired valve lift profiles into camshaft profiles, while a kinematic analysis is used to calculate piston to valve clearances and to define the practical limits of the PVO strategies. The NVO and PVO strategies are also compared to throttled SI operation at part load to assess the overall efficiency benefit of operating under the thermodynamic conditions of the SACI combustion regime. While the results of this study are engine specific, there are several camshaft profiles that are appropriate for the use of PVO rebreathing type valve events. For the range of PVO valve events examined and taking into consideration piston to valve interference, the use of high exhaust and low intake lifts with early exhaust valve opening timing and long PVO durations enables high levels of internal EGR with relatively low pumping losses.

A Cycle-to-Cycle Method to Predict HCCI Combustion Phasing

Homogeneous Charge Compression Ignition (HCCI) is a low temperature combustion strategy that simultaneously improves fuel efficiency and lowers engine-out NOx emissions. Unfortunately, broad usage of HCCI is hampered by combustion instabilities and a limited operation envelope. To help understand these limitations, this paper treats individual cylinders in a production four-cylinder engine as dynamical systems that iterate CA90 (the crank angle where 90% of net heat release is achieved) cycle-to-cycle as the engine operates in an unboosted, negative valve overlap HCCI combustion mode. This approach is shown to provide qualitative understanding of the stability limit bifurcation behavior, while also enabling quantitative cycle-to-cycle predictions of combustion phasing across a wide variety of transient and steady-state conditions, right up to complete misfire.

An Experimental Investigation of Reactivity-Controlled Compression Ignition Combustion in a Single-Cylinder Diesel Engine Using Hydrous Ethanol

Dual-fuel reactivity-controlled compression ignition (RCCI) combustion using port injection of a less reactive fuel and early-cycle direct injection of a more reactive fuel has been shown to yield both high thermal efficiency and low NOX and soot emissions over a wide engine operating range. Conventional and alternative fuels such as gasoline, natural gas and E85 as the lower reactivity fuel in RCCI have been studied by many researchers; however, published experimental investigations of hydrous ethanol use in RCCI are scarce. Making greater use of hydrous ethanol in internal combustion engines has the potential to dramatically improve the economics and life cycle carbon dioxide emissions of using bio-ethanol. In this work, an experimental investigation was conducted using 150 proof hydrous ethanol as the low reactivity fuel and commercially-available diesel as the high reactivity fuel in an RCCI combustion mode at various load conditions. A modified single-cylinder diesel engine was used for the experiments. Based on previous studies on RCCI combustion by other researchers, early-cycle split-injection strategy of diesel fuel was used to create an in-cylinder fuel reactivity distribution to maintain high thermal efficiency and low NOX and soot emissions. At each load condition, timing and mass fraction of the first diesel injection was held constant, while timing of the second diesel injection was swept over a range where stable combustion could be maintained. Since hydrous ethanol is highly resistant to auto-ignition and has large heat of vaporization, intake air heating was needed to obtain stable operations of the engine. The study shows that 150 proof hydrous ethanol can be used as the low reactivity fuel in RCCI through 8.6 bar IMEP and with ethanol energy fraction up to 75% while achieving simultaneously low levels of NOX and soot emissions. With increasing engine load, less intake heating is needed and EGR is required to maintain low NOX emissions. Future work will look at stability of hydrous ethanol RCCI at higher engine load.