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A detailed chemical model was implemented in the KIVA-3V two dimensional CFD code to investigate the effects of the spray cone angle and injection timing on the PCCI combustion process and emissions in an optical research diesel engine. A detailed chemical model for Primary Reference Fuel (PRF) consisting of 157 species and 1552 reactions was used to simulate diesel fuel chemistry. The model validation shows good agreement between the predicted and measured pressure and emissions data in the selected cases with various spray angles and injection timings. If the injection is retarded to -50° ATDC, the spray impingement at the edge of the piston corner with 100° injection angle was shown to enhance the mixing of air and fuel. The minimum fuel loss and more widely distributed fuel vapor contribute to improving combustion efficiency and lowering uHC and CO emissions in the engine idle condition.

This paper describes cyclic Air/Fuel ratio (AFR) measurements carried out with a novel device (fUEGO) based on a production Universal Exhaust Gas Oxygen sensor, but modified to give an improved frequency response. The results are compared to AFR calculated from a fast CO/CO2 analyser and a fast response flame ionization detector (FID). The direct comparison of the two different methods for determining the cyclic AFR reveals that the electrochemical device is in reasonable agreement with the more complex carbon balance method and can provide reliable cyclic AFR measurements with a reduced requirement for equipment and data post processing. The fUEGO however is sensitive to elevated levels of uHC's (unburned hydrocarbons) during misfires or partial burns and readings during such situations usually show deviations compared to the carbon balance method.

Three-dimensional Computational Fluid Dynamics (CFD) has become an integral part in analysing engine in-cylinder processes since it provides detailed information on the flow and combustion, which helps to find design improvements during the development of modern engine concepts. The predictive capability of simulation tools depends largely on the accuracy, fidelity and robustness of the various models used, in particular concerning turbulence and combustion. In this study, a flamelet model with a physics based closure for the progress variable dissipation rate is applied for the first time to a spark ignited IC engine. The predictive capabilities of the proposed approach are studied for one operating condition of a gasoline port fuel injected single-cylinder, four-stroke spark ignited full-metal engine running at 3,500 RPM close to full load (10 bar BMEP) at stoichiometric conditions.

Engines with reduced emissions and improved efficiency are of high interest for road transport. However, achieving these two goals is challenging and various concepts such as PFI/DI/HCCI/PCCI are explored by engine manufacturers. The computational fluid dynamics is becoming an integral part of modern engine development programme because this method provides access to in-cylinder flow and thermo-chemical processes to develop a closer understanding to tailor tumble and swirling motions to construct green engines. The combustion modelling, its accuracy and robustness play a vital role in this. Out of many modelling methods proposed in the past flamelet based methods are quite attractive for SI engine application. In this study, FlaRe (Flamelets revised for physical consistencies) approach is used to simulate premixed combustion inside a gasoline PFI single-cylinder, four-stroke SI engine. This approach includes a parameter representing the effects of flame curvature on the burning rate.

A multi-objective optimization scheme based on stochastic global search is developed and used to examine the performance of an HCCI model containing a reduced chemical kinetic mechanism, and to study interrelations among different model responses. A stochastic reactor model of an HCCI engine is used in this study, and dedicated HCCI engine experiments are performed to provide reference for the optimization. The results revealed conflicting trends among objectives normally used in mechanism optimization, such as ignition delay and engine cylinder pressure history, indicating that a single best combination of optimization variables for these objectives did not exist. This implies that optimizing chemical mechanisms to maintain universal predictivity across such conflicting responses will only yield a predictivity tradeoff. It also implies that careful selection of optimization objectives increases the likelihood of better predictivity for these objectives.

One of the limits on the maximum fuel efficiency benefit to be gained from turbocharged, downsized gasoline engines is the occurrence of low speed pre-ignition (LSPI). LSPI may lead to high pressures and extreme knock (megaknock or superknock) which can cause severe engine damage. Though the mechanism leading to megaknock is not completely resolved, LSPI is thought to arise from local auto-ignition of areas in the cylinder which are rich in low ignition delay “contaminants” such as engine oil and/or heavy ends of gasoline. These contaminants are introduced to the combustion chamber at various points in the engine cycle (e.g. entering from the top land crevice during blow-down or washed from the cylinder walls during DI wall impingement). This paper describes a method for testing the propensity of different contaminants to cause a local pre-ignition in a gasoline engine. During one cycle, a small amount of contaminant is injected into one cylinder of a 4 cylinder engine.

Premixed Charge Compression Ignition (PCCI), a Low Temperature Combustion (LTC) strategy for diesel engines is of increasing interest due to its potential to simultaneously reduce soot and NOx emissions. However, the influence of mixture preparation on combustion phasing and heat release rate in LTC is not fully understood. In the present study, the influence of injection timing on mixture preparation, combustion and emissions in PCCI mode is investigated by experimental and computational methods. A sequential coupling approach of 3D CFD with a Stochastic Reactor Model (SRM) is used to simulate the PCCI engine. The SRM accounts for detailed chemical kinetics, convective heat transfer and turbulent micro-mixing. In this integrated approach, the temperature-equivalence ratio statistics obtained using KIVA 3V are mapped onto the stochastic particle ensemble used in the SRM.

One of the limits on the maximum fuel efficiency benefit to be gained from turbocharged, downsized gasoline engines is the occurrence of pre-ignitions at low engine speed. These pre-ignitions may lead to high pressures and extreme knock (megaknock or superknock) which can cause severe engine damage. Though the mechanism leading to megaknock is not completely resolved, pre-ignitions are thought to arise from local autoignition of areas in the cylinder which are rich in low ignition delay “contaminants” such as engine oil and/or heavy ends of gasoline. These contaminants are introduced to the combustion chamber at various points in the engine cycle (e.g. entering from the top land crevice during blow-down or washed from the cylinder walls during DI wall impingement).

Highly homogeneous compression ignition is difficult to achieve in a direct injection diesel engine. The difficulty of achieving adequate fuel vaporization and the problems of fuel spray wall impingement are the main factors. Limitation of the maximum operating load results from high rates of pressure rise that occur in this combustion regime. The levels of HC and CO emissions are raised substantially when compared with conventional combustion and remain a significant emission factor. In this study, two methods of achieving highly homogeneous combustion in a direct injection diesel engine were investigated, Nissan MK type and early injection. The effects of fuel injection pressure, injection timing, EGR level, EGR cooler efficiency and compression ratio were examined using a conventional 4 cylinder 2.0L common rail diesel engine with 18.4:1 and 14.4:1 compression ratios.

A dual-fuel approach to control combustion in HCCI engine is investigated in this work. This approach involves controlling the combustion heat release rate by adjusting fuel reactivity according to the conditions inside the cylinder. Experiments were performed on a single-cylinder research engine fueled with different ratios of primary reference fuels and operated at different speed and load conditions, and results from these experiments showed a clear potential for the approach to expand the HCCI engine operation window. Such potential is further demonstrated dynamically using an optimized stochastic reactor model integrated within a MATLAB code that simulates HCCI multi-cycle operation and closed-loop control of fuel ratio. The model, which utilizes a reduced PRF mechanism, was optimized using a multi-objective genetic algorithm and then compared to a wide range of engine data.

The objective of this study was to examine the operating characteristics of a light duty multi cylinder compression ignition engine with regular gasoline fuel at low engine speed and load. The effects of fuel stratification by means of multiple injections as well as the sensitivity of auto-ignition and burn rate to intake pressure and temperature are presented. The measurements used in this study included gaseous emissions, filter smoke opacity and in-cylinder indicated information. It was found that stable, low emission operation was possible with raised intake manifold pressure and temperature, and that fuel stratification can lead to an increase in stability and a reduced reliance on increased temperature and pressure. It was also found that the auto-ignition delay sensitivity of gasoline to intake temperature and pressure was low within the operating window considered in this study.

Large-bore natural gas engines may use pre-chamber ignition. Despite extensive research in engine environments, the exact nature of the jet, as it exits the pre-chamber orifice, is not thoroughly understood and this leads to uncertainty in the design of such systems. In this work, a specially-designed rig comprising a quartz pre-chamber fit with an orifice and a turbulent flowing mixture outside the pre-chamber was used to study the pre-chamber flame, the jet, and the subsequent premixed flame initiation mechanism by OH* and CH* chemiluminescence. Ethylene and methane were used. The experimental results are supplemented by LES and 0D modelling, providing insights into the mass flow rate evolution at the orifice and into the nature of the fluid there. Both LES and experiment suggest that for large orifice diameters, the flow that exits the orifice is composed of a column of hot products surrounded by an annulus of unburnt pre-chamber fluid.

A standard port fuel injected, unthrottled single cylinder four-stroke SI engine, with a compression ratio of 10.3:1, and using standard gasoline fuel, has been adapted to operate in the homogeneous charge compression ignition (HCCI) mode, by modifying the valve timing. It has been found that over a speed range of between 1300 and 2000 rpm, and lambda values of between 0.95 and 1.1, stable operation is achieved without spark ignition. The internal EGR rate was estimated to be about 60%, and emissions of NOX were typically 0.25 g/kWh. Practical implementation of this HCCI concept will require variable valve timing, which will also enable reversion to standard SI operation for maximum power.

A heavy-duty diesel engine (ETH-LAV single cylinder MTU396 heavy duty research engine) was simulated by RANS and advanced reacting flow models to gain insight into its soot and NOx emissions. Due to symmetry, a section of the engine containing a single injector-hole was simulated. Dodecane was used as a surrogate to emulate the evaporation properties of diesel and a 22-step reaction mechanism for n-heptane was used to describe combustion. The Conditional Moment Closure (CMC) method was used as the combustion model in two ways. In a more conventional modelling approach, CMC was fully interfaced with the CFD and a two-equation model was employed for determining soot while the extended Zeldovich mechanism was used for NOx. In a second approach called the Imperfectly Stirred Reactor (ISR) method, the CMC equation was integrated over space and the previous RANS-CMC solution was further analysed in a post-processing step with the focus on soot.

The information provided by the in-cylinder pressure signal is of great importance for modern engine management systems. The obtained information is implemented to improve the control and diagnostics of the combustion process in order to meet the stringent emission regulations and to improve vehicle reliability and drivability. The work presented in this paper covers the experimental study and proposes a comprehensive and practical solution for the estimation of the in-cylinder pressure from the crankshaft speed fluctuation. Also, the paper emphasizes the feasibility and practicality aspects of the estimation techniques, for the real-time online application. In this study an engine dynamics model based estimation method is proposed. A discrete-time transformed form of a rigid-body crankshaft dynamics model is constructed based on the kinetic energy theorem, as the basis expression for total torque estimation.

A turbulent combustion model is described for SI engines with large variations in mixture strength. The model is for a single gas phase fluid at high Reynolds number and treats combustion in the laminar flamelet regime, which is characterized by high Damkholer and low Karlovitz numbers. An assumed probability density function (pdf) approach is used to extract expressions for mean quantities of interest, which are parameterized on the progress variable and mixture fraction variables. A double delta function pdf is used for the reaction progress variable and a beta function pdf is used for the mixture fraction. The reaction rate term in the progress variable equation is closed using an algebraic expression, which incorporates the effects of mixture strength, pressure and temperature on laminar flame speed. The model is implemented in two versions of a Computational Fluid Dynamics (CFD) code.

Simple air-path models for modern (VGT/EGR equipped) diesel engines are in common use, and have been reported in the literature. This paper addresses some of the shortcomings of control-oriented models to allow better prediction of the cylinder charge properties. A fast response CO2 analyzer is used to validate the model by comparing the recorded and predicted CO2 concentrations in both the intake port and exhaust manifold of one of the cylinders. Data showing the recorded NOx emissions and exhaust gas opacity during a step change in engine load illustrate the spikes in both NOx and smoke seen during transient conditions. The predicted cylinder charge properties from the model are examined and compared with the measured NOx and opacity. Together, the emissions data and charge properties paint a consistent picture of the phenomena occurring during the transient. Alternative strategies for the fueling and cylinder charge during these load transients are investigated and discussed.

The underbody of a truck is responsible for an appreciable portion of the vehicle’s aerodynamic drag, and thus its fuel consumption. A better understanding of the underbody aerodynamics could lead to designs that are more environmentally friendly. Unfortunately there are difficulties with correctly replicating the ground condition and rotating wheels when using the classical approach of a wind-tunnel for aerodynamic investigation. This in turn leads to computational modelling problems. A lack of experimental data for Computational Fluid Dynamics (CFD) validation means that the flow field in this area has seldom been investigated. There is thus very little information available for the optimisation and design of underbody aerodynamic devices. This paper investigates the use of a water-towing tank, which allows the establishment of the correct near-ground flow while permitting good optical access. Using a 1/10 scale model, Reynolds Numbers of around 0.7 million are achieved.

The cylinder pressure signal, as an instantaneous and direct measure of the engine operation, contains valuable information for closed loop engine control and offers very useful engine monitoring and control capabilities. The estimation technique for cylinder pressure has been investigated for many years. Based on the Frequency Analysis Method, a synthetic estimation method is proposed in this paper to estimate pressure. Methods that are successful in obtaining a more accurate estimated cylinder pressure over a wider range of crankshaft angle are reported. Quantitative results obtained from application of the method are also given.