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Boosted Homogeneous Charge Compression Ignition (HCCI) has been modeled and has demonstrated the potential to extend the engine's upper load limit. A commercially available engine simulation software (GT-PowerÖ) coupled to the University of Michigan HCCI combustion and heat transfer correlations was used to model a 4-cylinder boosted HCCI engine with three different boosting configurations: turbocharging, supercharging and series turbocharging. The scope of this study is to identify the best boosting approach in order to extend the HCCI engine's operating range. The results of this study are consistent with the literature: Boosting helps increase the HCCI upper load limit, but matching of turbochargers is a problem. In addition, the low exhaust gas enthalpy resulting from HCCI combustion leads to high pressures in the exhaust manifold increasing pumping work. The series turbocharging strategy appears to provide the largest load range extension.

Stringent fuel economy and emissions regulations have driven development of new mixture preparation technologies and increased spark-ignition engine complexity. Additional degrees of freedom, brought about by devices such as cam phasers and charge motion control valves, enable greater range and flexibility in engine control. This permits significant gains in fuel efficiency and emission control, but creates challenges related to proper engine control and calibration techniques. Accurate experimental characterization of high degree of freedom engines is essential for addressing the controls challenge. In particular, this paper focuses on the evaluation of three experimental residual gas fraction measurement techniques for use in a spark ignition engine equipped with dual-independent variable camshaft phasing (VVT).

A study has been conducted in order to investigate the effect of the location of knock initiation on heat flux in a Spark-Ignition (SI) combustion chamber. Heat flux measurements were taken on the piston and cylinder head under different knock intensity levels, induced by advancing the spark timing. Tests were performed with two engine configurations, the first with the spark-plug located on the rear side of the chamber and the other having a second non-firing spark-plug placed at the front side of the chamber. The presence of the non-firing spark-plug consistently shifted the location of autoignition initiation from the surface of the piston to its vicinity, without causing a noticeable increase in knock intensity. By localizing the initiation of knock, changes induced in the secondary flame propagation pattern affected both the magnitude and the rate of change of peak heat flux under heavy knock.

A detailed chemical kinetic mechanism, consisting of 22 species and 104 elementary reactions, has been used in conjunction with the multi-dimensional reactive flow code KIVA-3 to study autoignition of natural gas injected under compression ignition conditions. Calculations for three different blends of natural gas are performed on a three-dimensional computational grid by modeling both the injection and ignition processes. Ignition delay predictions at pressures and temperatures typical of top-dead-center conditions in compression ignition engines compare well with the measurements of Naber et al. [1] in a combustion bomb. Two different criteria, based on pressure rise and mass of fuel burned, are used to detect the onset of ignition. Parametric studies are conducted to show the effect of additives like ethane and hydrogen peroxide in increasing the fuel consumption rate.

A comprehensive methodology for predicting the transient thermal response of spark-ignition engines subject to time-varying boundary conditions is presented. The approach is based on coupling a cycle-resolved quasi-dimensional simulation of in-cylinder thermodynamic events with a resistor-capacitor (R-C) thermal network of the various component and fluid interactions throughout the engine and exhaust system. The dynamic time step of the thermal solution is limited by either the frequency of the prescribed time-dependent boundary conditions or by the minimum thermal time constant of the R-C network. To demonstrate the need for fully-coupled, transient thermodynamic and heat transfer solutions, model behavior is first explored for step-change and staircase variations of engine operating conditions.

An experimental study of the effects of thin ceramic thermal barrier coatings on the performance of a spark-ignited gasoline engine was conducted. A modified 2.5 liter GM engine with ceramic-coated pistons, liners, head, valves and ports was used. Experimental results obtained from the ceramic engine were compared with baseline metal engine data. It was shown that at low-speed part-load conditions encountered in typical driving cycles the ceramic engine could achieve up to 18% higher brake power and up to 10% lower specific fuel consumption. At wide open throttle conditions, the two engines exhibited similar characteristics, except at high speeds where the metal engine showed better performance at the expense of inferior fuel economy. The ceramic coating did not produce any observable knock in the engine and showed no significant wear at the conclusion of the testing phase.

The thermal conditions of an engine structure, in particular the wall temperatures, have been shown to have a great effect on the HCCI engine combustion timing and burn rates through wall heat transfer, especially during transient operations. This study addresses the effects of thermal inertia on combustion in an HCCI engine. In this study, the control of combustion timing in an HCCI engine is achieved by modulating the residual gas fraction (RGF) while considering the wall temperatures. A multi-cylinder engine simulation with detailed geometry is carried out using a 1-D system model (GT-Power®) that is linked with Simulink®. The model includes a finite element wall temperature solver and is enhanced with original HCCI combustion and heat transfer models. Initially, the required residual gas fraction for optimal BSFC is determined for steady-state operation. The model is then used to derive a map of the sensitivity of optimal residual gas fraction to wall temperature excursions.

Extending the operating range of the gasoline HCCI engine is essential for achieving desired fuel economy improvements at the vehicle level, and it requires deep understanding of the thermal conditions in the cylinder. Combustion chamber deposits (CCD) have been previously shown to have direct impact on near-wall phenomena and burn rates in the HCCI engine. Hence, the objectives of this work are to characterize thermal properties of deposits in a gasoline HCCI engine and provide foundation for understanding the nature of their impact on autoignition and combustion. The investigation was performed using a single-cylinder engine with re-induction of exhaust instrumented with fast-response thermocouples on the piston top and the cylinder head surface. The measured instantaneous temperature profiles changed as the deposits grew on top of the hot-junctions.

The number of control actuators available on spark-ignition engines is rapidly increasing to meet demand for improved fuel economy and reduced exhaust emissions. The added complexity greatly complicates control strategy development because there can be a wide range of potential actuator settings at each engine operating condition, and map-based actuator calibration becomes challenging as the number of control degrees of freedom expand significantly. Many engine actuators, such as variable valve actuation and flow control valves, directly influence in-cylinder combustion through changes in gas exchange, mixture preparation, and charge motion. The addition of these types of actuators makes it difficult to predict the influences of individual actuator positioning on in-cylinder combustion without substantial experimental complexity.

Adjusting the Residual Gas Fraction (RGF) by means of Variable Valve Actuation (VVA) is a strong candidate for controlling the ignition timing in Homogeneous Charge Compression Ignition (HCCI) engines. However, at high levels of residual gas fraction, insufficient mixing can lead to the presence of considerable temperature and composition variations. This paper extends previous modeling efforts to include the effect of RGF distribution on the onset of ignition and the rate of combustion using a multi-dimensional fluid mechanics code (KIVA-3V) sequentially with a multi-zone code with detailed chemical kinetics. KIVA-3V is used to simulate the gas exchange processes, while the multi-zone code computes the combustion event. It is shown that under certain conditions the effect of composition stratification is significant and cannot be captured by a single-zone model or a multi-zone model using only temperature zones.

The Homogeneous Charge Compression Ignition (HCCI) combustion concept is currently under widespread investigation due to its potential to increase thermal efficiency while greatly decreasing harmful exhaust pollutants. Simulation tools have been developed to explore the implications of initial mixture thermodynamic state on engine performance and emissions. In most cases these modeling efforts have coupled a detailed fuel chemistry mechanism with empirical descriptions of the in-cylinder heat transfer processes. The primary objective of this paper is to present a fundamentally based boundary layer heat transfer model. The two-zone combustion model couples an adiabatic core zone with a boundary layer heat transfer model. The model predicts film coefficient, with approximately the same universal shape and magnitudes as an existing global model.

Natural gas quality, in terms of the volume fraction of higher hydrocarbons, strongly affects the auto-ignition characteristics of the air-fuel mixture, the engine performance and its controllability. The influence of natural gas composition on engine operation has been investigated both experimentally and through chemical kinetic based cycle simulation. A range of two component gas mixtures has been tested with methane as the base fuel. The equivalence ratio (0.3), the compression ratio (19.8), and the engine speed (1000 rpm) were held constant in order to isolate the impact of fuel autoignition chemistry. For each fuel mixture, the start of combustion was phased near top dead center (TDC) and then the inlet mixture temperature was reduced. These experimental results have been utilized as a source of data for the validation of a chemical kinetic based full-cycle simulation.

When automobile hydrocarbons are exhausted into the atmosphere in the presence of NOx and sunlight, ground-level ozone is formed. While researchers have used Maximum Incremental Reactivity (MIR) factors to estimate ozone production, this procedure often overestimates Local Ozone Production (LOP) because it does not consider local atmospheric conditions. In this paper, an enhanced MIR methodology for estimating actual LOP attributable to a vehicle in a particular ozone problem area is presented. In addition to using tabulated MIR factors, the procedure also uses local hydrocarbon reaction terms and a relative mechanistic reactivity term that account for local atmospheric conditions. Through this approach, the effects of hydrocarbon reaction rates, hydrocarbon residence times, and prevailing HC/NOx ratio are accounted for. The procedure is intended to enable automotive engineers to more realistically estimate actual local ozone production resulting from hydrocarbon emissions.

This paper discusses the compression ratio influence on maximum load of a Natural Gas HCCI engine. A modified Volvo TD100 truck engine is controlled in a closed-loop fashion by enriching the Natural Gas mixture with Hydrogen. The first section of the paper illustrates and discusses the potential of using hydrogen enrichment of natural gas to control combustion timing. Cylinder pressure is used as the feedback and the 50 percent burn angle is the controlled parameter. Full-cycle simulation is compared to some of the experimental data and then used to enhance some of the experimental observations dealing with ignition timing, thermal boundary conditions, emissions and how they affect engine stability and performance. High load issues common to HCCI are discussed in light of the inherent performance and emissions tradeoff and the disappearance of feasible operating space at high engine loads.

In this paper, the available correlations proposed in the literature for the gas-side heat transfer in the intake and exhaust system of a spark-ignition internal combustion engine were surveyed. It was noticed that these only by empirically fitted constants. This similarity provided the impetus for the authors to explore if a universal correlation could be developed. Based on a scaling approach using microscales of turbulence, the authors have fixed the exponential factor on the Reynolds number and thus reduced the number of adjustable coefficients to just one; the latter can be determined from a least squares curve-fit of available experimental data. Using intake and exhaust side data, it was shown that the universal correlation The correlation coefficient of this proposed heat transfer model with all available experimental data is 0.845 for the intake side and 0.800 for the exhaust side.

The present study introduces a modeling approach for investigating the effects of valve events and gas exchange processes in the framework of a full-cycle HCCI engine simulation. A multi-dimensional fluid mechanics code, KIVA-3V, is used to simulate exhaust, intake and compression up to a transition point, before which chemical reactions become important. The results are then used to initialize the zones of a multi-zone, thermo-kinetic code, which computes the combustion event and part of the expansion. After the description and the validation of the model against experimental data, the application of the method is illustrated in the context of variable valve actuation. It has been shown that early exhaust valve closing, accompanied by late intake valve opening, has the potential to provide effective control of HCCI combustion.

Selective Catalytic Reduction (SCR) catalysts used in Lean NOx Trap (LNT) - SCR exhaust aftertreatment systems typically encounter alternating oxidizing and reducing environments. Reducing conditions occur when diesel fuel is injected upstream of a reformer catalyst, generating high concentrations of hydrogen (H₂), carbon monoxide (CO), and hydrocarbons to deNOx the LNT. In this study, the functionality of an iron (Fe) zeolite SCR catalyst is explored with a bench top reactor during steady-state and cyclic transient SCR operation. Experiments to characterize the effect of an LNT deNOx event on SCR operation show that adding H₂ or CO only slightly changes SCR behavior with the primary contribution being an enhancement of nitrogen dioxide (NO₂) decomposition into nitric oxide (NO). Exposure of the catalyst to C₃H₆ (a surrogate for an actual exhaust HC mixture) leads to a significant decrease in NOx reduction capabilities of the catalyst.

Exhaust gas rebreathing is considered to be a practical enabler that could be used in HCCI production engines. Recent experimental work at the University of Michigan demonstrates that the combustion characteristics of an HCCI engine using large amounts of hot residual gas by rebreathing are very sensitive to engine thermal conditions. This computational study addresses HCCI engine operation with rebreathing, with emphasis on the effects of engine thermal conditions during transient periods. A 1-D cycle simulation with thermal networks is carried out under load and speed transitions. A knock integral auto-ignition model, a modified Woschni heat transfer model for HCCI engines and empirical correlations to define burn rate and combustion efficiency are incorporated into the engine cycle simulation model. The simulation results show very different engine behavior during the thermal transient periods compared with steady state.

A semi-empirical engine piston/ring assembly friction model based on the concept of the Stribeck diagram and similarity analysis is described. The model was constructed by forming non-dimensional parameters based on design and operating conditions. Friction data collected by the Fixed-Sleeve method described in [1]* at one condition, were used to correlate the coefficient of friction of the assembly and the other non-dimensional parameters. Then, using the instantaneous cylinder pressure as input together with measured and calculated design and operating parameters, reasonable assembly friction and fmep predictions were obtained for a variety of additional conditions, some of which could be compared with experimental values. Model inputs are component dimensions, ring tensions, piston skirt spring constant, piston skirt thermal expansion, engine temperatures, speed, load and oil viscosity.

The valve train was instrumented to record the instantaneous roller speed, roller pin friction torque, pushrod forces, and cam speed. Results are presented for one exhaust valve of a motored Cummins L-10 engine. The instantaneous cam/roller friction force was determined from the instantaneous roller speed and the pin friction torque. The pushrod force and displacement were also measured. Friction work loss was determined for both cam and roller interface as well as the upper valve train which includes the valve pushrod, rocker arm, valve guide, and valve. Roller follower slippage on the cam was also determined. A kinematic analysis with the measured data provided the normal force and contact stress at cam/roller interface.(1) Finally, the valve train friction was found to be in the mixed lubrication regime.(2) Further efforts will address the theoretical analysis of valve train friction to predict roller slippage.