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This paper presents a newly developed quasi-dimensional multi-zone dual fuel combustion model, which has been integrated within the commercial engine system simulation framework. Model is based on the modified Multi-Zone Combustion Model and Fractal Combustion Model. Modified Multi-Zone Combustion Model handles the part of the combustion process that is governed by the mixing-controlled combustion, while the modified Fractal Combustion Model handles the part that is governed by the flame propagation through the combustion chamber. The developed quasi-dimensional dual fuel combustion model features phenomenological description of spray processes, i.e. liquid spray break-up, fresh charge entrainment, droplet heat-up and evaporation process. In order to capture the chemical effects on the ignition delay, special ignition delay table has been made.

Development of SI engines to further increase engine efficiency is strongly affected by the occurrence of engine knock. Engine knock has been widely investigated over the years and the main promoting parameters have been identified as load (temperature and pressure), mixture composition, engine speed, characteristic of the fuel, combustion chamber design, and etc. In this paper a new model for predicting engine knock in 0-D environment is presented. The model is based on the well-known approach of using a Livengood and Wu knock integral. Ignition delay data that are supplied to the knock integral are for specific fuel calculated by detail chemical kinetics and are comprised of low temperature heat release ignition delay and high temperature heat release ignition delay. Next, the cycle to cycle variations of engine and temperature stratification of the end gas have to be taken into account.

Today, the potential of HCCI engines, i.e., their high efficiency with low NO and particulate emissions, is very well known. Besides this potential, the problems that are related to HCCI engines, particularly the control, are also known issues. In order to be able to develop and assess the control strategies for HCCI engines, one needs models for the control development. In addition to mean value models crank-angle resolved control-oriented computer codes have also been developed lately (e.g., Boost RT). In these codes, complex 1D gas dynamics and complex combustion models are omitted, while the in-cylinder calculation is crank-angle resolved. Simple combustion models are variations of Vibe and the combustion defined by a table. Since the HCCI combustion is controlled by the state of the gas in the cylinder, parameters of Vibe functions depend on the factors that define this state.

The paper presents the optimization of injection parameters of directly injected fuel in the dual fuel engine operation. The optimization is performed numerically by using a cycle simulation model of the considered engine. In the cycle simulation model, combustion is simulated by a newly developed quasi-dimensional dual fuel combustion model. The model is based on the modified multi-zone combustion model and the quasi-dimensional combustion model. The modified multi-zone combustion model handles the part of the combustion process that is governed by the mixing-controlled combustion, while the modified quasi-dimensional combustion model handles the part that is governed by the flame propagation through the combustion chamber. The developed dual fuel combustion model features a phenomenological description of spray processes, i.e. the liquid spray break-up, fresh charge entrainment, droplet heat-up, and evaporation processes.

Research into internal combustion engines requires the development of engine simulation models which should ensure acceptable results of engine performances over a wide range of engine speeds and loads. Due to high costs of experiments and a rapid increase in the computer power, researches all over the world devote great effort to the development and improvement of simulation models. Well-known multi-dimensional simulation models (CFD models) of the engine cycle are the most demanding models in terms of computational resources. On the other hand, there are multi-zone models that are very robust and that are able to capture a certain in-cylinder property during the engine operating cycle. It is known that turbulence effects inside engine cylinder play an important role in the combustion process. In order to properly predict combustion process, characteristics of the turbulent flow field should also be accurately defined.

The paper presents the experimental study of an active pre-chamber volume variations on engine performance and emissions. The experiments were performed on a test setup equipped with a single cylinder engine. The modular and custom-made pre-chamber design was used, enabling the variation of pre-chamber volume in the range of 3-5% of clearance volume. During the variation of pre-chamber’s geometrical parameters, the ratio of total nozzle area to the pre-chamber volume was fixed at a value of approximately 0.033 cm-1. At a given pre-chamber volume the variation of engine load was achieved by the change of excess air ratio in the main chamber from stochiometric mixture to lean limit, while the engine speed was fixed to 1600 rpm. For each pre-chamber variation and on each of the investigated operating points, a spark sweep was performed to obtain the highest indicated efficiency while satisfying the imposed restrictions regarding combustion stability and knock occurrence.

This paper follows a cycle-simulation method for creating an engine performance map for an ethanol fueled boosted HCCI engine using a 1-dimensional engine model. Based on experimentally determined limits, the study defined operating conditions for the engine and performed a limited parameter sweep to determine the best efficiency case for each condition. The map is created using a 6-Zone HCCI combustion model coupled with a detailed chemical kinetic reaction mechanism for ethanol, and validated against engine data collected from a 1.9L 4-Cylinder VW TDI engine modified to operate in HCCI mode. The engine was mapped between engine speeds of 900 and 3000 rpm, 1 and 3 bar intake pressure, and 0.2 and 0.4 equivalence ratio, resulting in loads between idle and 14.0 bar BMEP. Analysis of a number of trends for this specific engine map are presented, such as efficiency trends, effects of combustion phasing, intake temperature, engine load, engine speed, and operating strategy.

The paper presents modeling of cycle-to-cycle variations (CCV) of a SI engine by using the modified cycle-simulation model. The presented research has been performed on CFR engine fueled by gasoline. Experimental in-cylinder pressure traces of 300 cycles have been processed for several operating points representing the spark sweep which captured the operating points with low and high CCV. The cycle-simulation model applied in this study uses significantly improved turbulence and combustion model that have been implemented into the cycle-simulation code. Developed k-ε turbulence model and the quasi-dimensional combustion model based on the fractal theory have been applied.

Nowadays, the main potential of the HCCI engine, i.e. high efficiency with low NOx and soot emissions, is a well-known fact. Main limitations that prevent the commercial application of the HCCI engine are the control of combustion timing and low power density. Higher power density could be achieved by boosting the engine, but low exhaust temperatures associated with the HCCI combustion require a different approach when trying to achieve a boosted HCCI engine. This paper presents a numerical study on two boosting configurations that will enable high boost levels and high load, as a consequence, in the Ethanol fueled HCCI engine, in the engine speed range of 1000 - 4000 rpm. For the purposes of this study, a four-cylinder HCCI engine model has been made in the cycle-simulation software. The model includes the entire engine geometry and all elements necessary for representing the entire engine flow path.

In the paper the operation of a turbocharged dual fuel engine at mid-high load is investigated on a single cylinder experimental engine complemented by a full 0D/1D simulation model that provides boundary conditions for the experiment and full engine system results. When duel fuel combustion mode is used on a turbocharged engine with the variable geometry turbocharger, the mid-high load operating points can be obtained with number of different combinations of intake pressure and excess air ratio. Besides the impact on combustion, the specific combination of intake pressure - excess air ratio has also impact on the exhaust back pressure caused by the turbocharger and consequently on the obtained brake efficiency. Additionally, the dual fuel combustion is influenced by natural gas mass fraction and start of injection of diesel fuel and the search for the optimal solution could be a challenging task.

The paper evaluates different strategies of dual fuel (DF) operation in search of a solution that enables DF at low load. The strategies that were explored are conventional DF with increased intake temperature, split injection, and reactivity controlled compression ignition (RCCI) combustion. The RCCI operation enabled DF operation at higher natural gas mass fractions, with higher efficiency, and lower THC, CO and NOX emissions than in DF operation, while the efficiency of normal diesel operation (NDO) remained highest. If CO2 emission or cost effectiveness is used as a measure of performance then RCCI provided better performance than NDO as well.

A promising strategy for increasing thermal efficiency and decreasing emissions of a spark ignited (SI) internal combustion engine is the application of lean mixtures. The flammability limit of lean mixtures can be increased by using an active pre-chamber containing an injector and a spark plug, resulting in a combustion mode commonly called Turbulent Jet Ignition (TJI). The optimization of the combustion chamber shape and operating parameters for TJI combustion can be a demanding task, since the number of design parameters is significantly increased and is today supported by numerical simulations. In this paper, the process of the development of a numerical framework based on 3D CFD and 1D/0D numerical models that will support the research of the pre-chamber design and optimization of operating parameters will be shown. For 3D CFD modelling the AVL Fire™ code is employed, where the full combustion chamber model with intake and exhaust ports of the experimental engine is prepared.

It is a well-known fact that HCCI combustion offers the possibility of achieving high efficiency with low emissions, but with the challenges in combustion control and ability to adjust to changing environmental conditions. To resolve the aforementioned challenges, a pre-chamber induced homogeneous charge compression ignition (PC-HCCI) combustion mode was experimentally tested with aim of providing initial operating boundaries in terms of combustion stability and obtaining initial performance results. The single cylinder engine equipped with active pre-chamber and compression ratio (CR) of 17.5 was fueled by gasoline. The initial experiments were performed at the engine speed of 1600 rpm with intake air temperatures varied from 33°C to 100°C to verify the possibility of achieving the PC-HCCI combustion mode and to compare the achieved engine performance and emission results with both PCSI and pure HCCI combustion modes used as reference cases.

Homogeneous charge compression ignition (HCCI) in natural gas fueled engines is thought to achieve high efficiency and low NOx emissions. While automotive applications require various load and speed regions, the operation range of stationary cogeneration engines is narrower. Hence, HCCI operation is easier to reach and more applicable to comply with future emission standards. This study presents computationally investigations of the auto-ignition ranges of a stationary natural gas HCCI engine. Starting from a detailed 1D engine cycle simulation model, a reduced engine model was developed and coupled to chemical kinetics using AVL Boost. Compression ratio, air-fuel ratio, internal EGR rate (iEGR) and intake temperature were varied for three different speeds, namely 1200, 1700 and 2200 rpm. Each examination includes a full factorial design study of 375 configurations. In the first step, the combustion was calculated using the GRI-mechanism 3.0 and a single zone combustion model.

Advanced combustion concepts that rely on the lean-burn approach are a proven solution for increasing the efficiency and reducing the harmful emissions of SI engines. The pre-chamber spark ignited (PCSI) engines utilize high ignition energy of the multiple jets penetrating from the pre-chamber, to enable fast and stable combustion of lean mixture in the main chamber. The combustion is still governed by the flame propagation, so the dilution level and efficiency benefits are highly restricted by strong decrease of laminar flame speeds. Homogeneous charge compression ignition (HCCI) combustion allows a higher dilution level due to rapid chemically driven combustion, however the inability to directly control the ignition timing has proven to be a major setback in HCCI deployment.