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In the study presented in this paper, a vehicle driving cycle simulation of the pneumatic hybrid has been conducted. The pneumatic hybrid powertrain has been modeled in GT-Power and validated against experimental data. The GT-Power engine model has been linked with a MATLAB/simulink vehicle model. The engine in question is a single-cylinder Scania D12 diesel engine, which has been converted to work as a pneumatic hybrid. The base engine model, provided by Scania, is made in GT-power and it is based on the same engine configuration as the one used in real engine testing. During pneumatic hybrid operation the engine can be used as a 2-stroke compressor for generation of compressed air during vehicle deceleration and during vehicle acceleration the engine can be operated as a 2-stroke air-motor driven by the previously stored pressurized air.

Variable compression ratio (VCR) technology has long been recognized as a method for improving the automobile engine performance, efficiency, fuel economy with reduced emission. This paper presents a design of hydraulically actuated piston based on the VCR piston proposed by the British Internal Combustion Engine Research Institute (BICERI). In this design, the compression height of the piston automatically changes in response to engine cylinder pressure by controlling the lubrication oil flow via valves in the piston. In addition, numerical models including piston kinetic model, oil hydraulic model, compression ratio model and etc., have been established to evaluate the piston properties. The oil flow characteristics between two chambers in VCR piston have been investigated and the response behaviors of VCR engine and normal engine, such as compression pressure and peak cylinder pressure, are compared at different engine loads.

The heavy-duty diesel engine industry is required to meet stringent emission standards. There is also the demand for more fuel efficient engines by the customer. In a previous study on an engine with variable intake valve closure timing, the authors found that an early single injection and accompanying premixed charge compression ignition (PCCI) combustion provides advantages in emissions and fuel economy; however, unacceptably high peak pressures and rates of pressure-rise impose a severe operating constraint. The use of a Pressure Reactive Piston assembly (PRP) as a means to limit peak pressures is explored in the present work. The concept is applied to a heavy-duty diesel engine and genetic algorithms (GA) are used in conjunction with the multi-dimensional engine simulation code KIVA-3V to provide an optimized set of operating variables.

This study applies a state feedback based Closed-Loop Combustion Control (CLCC) using Fast Thermal Management (FTM) on a multi cylinder Variable Compression Ratio (VCR) engine. At speeds above 1500 rpm is the FTM's bandwidth broadened by using the VCR feature of this engine, according to a predefined map, which is a function of load and engine speed. Below 1500 rpm is the PID based CLCC using VCR applied instead of the FTM while slow cylinder balancing is effectuated by the FTM. Performance of the two CLCC controllers are evaluated during an European EC2000 drive cycle, while HC, CO and CO2 emissions are measured online by a Fast Response Infrared (FRI) emission equipment. A load and speed map calculated for an 1.6L Opel Astra is used to get reference values for the dynamometer speed and the load control. The drive cycle test is initiated from a hot engine and hence no cold start is included. Commercial RON/MON 92/82 gasoline, which corresponds to US regular, is utilized.

Simultaneous two-component measurements of gas velocity and multi-dimensional numerical simulation are employed to characterize the evolution of the in-cylinder turbulent flow structure in a re-entrant bowl-in-piston engine under motored operation. The evolution of the mean flow field, turbulence energy, turbulent length scales, and the various terms contributing to the production of the turbulence energy are correlated and compared, with the objectives of clarifying the physical mechanisms and flow structures that dominate the turbulence production and of identifying the source of discrepancies between the measured and simulated turbulence fields. Additionally, the applicability of the linear turbulent stress modeling hypothesis employed in the k-ε model is assessed using the experimental mean flow gradients, turbulence energy, and length scales.

The different roles played by small and large eddies in engine combustion were studied. Experiments compared natural gas combustion in a converted, single cylinder Volvo TD 102 engine and in a 125 mm cubical cell. Turbulence is used to enhance flame growth, ideally giving better efficiency and reduced cyclic variation. Both engine and test cell results showed that flame growth rate correlated best with the level of high frequency, small eddy turbulence. The more effective, small eddy turbulence also tended to lower cyclic variations. Large scales and bulk flows convected the flame relative to cool surfaces and were most important to the initial flame kernel.

In-cylinder flow and combustion processes simulated with the standard k-ε turbulence model and with an alternative model-employing a non-linear, quadratic equation for the turbulent stresses-are contrasted for both motored and fired engine operation at two loads. For motored operation, the differences observed in the predictions of mean flow development are small and do not emerge until expansion. Larger differences are found in the spatial distribution and magnitude of turbulent kinetic energy. The non-linear model generally predicts lower energy levels and larger turbulent time scales. With fuel injection and combustion, significant differences in flow structure and in the spatial distribution of soot are predicted by the two models. The models also predict considerably different combustion efficiencies and NOx emissions.

In-cylinder fluid velocity is measured in an optically accessible, fired HSDI engine at idle. The velocity field is also calculated, including the full induction stroke, using multi-dimensional fluid dynamics and combustion simulation models. A detailed comparison between the measured and calculated velocities is performed to validate the computed results and to gain a physical understanding of the flow evolution. Motored measurements are also presented, to clarify the effects of the fuel injection process and combustion on the velocity field evolution. The calculated mean in-cylinder angular momentum (swirl ratio) and mean flow structures prior to injection agree well with the measurements. Modification of the mean flow by fuel injection and combustion is also well captured.

To overcome the trade-off between NOx and particulate emissions for future diesel vehicles and engines it is necessary to seek methods to lower pollutant emissions. The desired simultaneous improvement in fuel efficiency for future DI (Direct Injection) diesels is also a difficult challenge due to the combustion modifications that will be required to meet the exhaust emission mandates. This study demonstrates the emission reduction capability of split injections, EGR (Exhaust Gas Recirculation), and other parameters on a High Speed Direct Injection (HSDI) diesel engine equipped with a common rail injection system using an RSM (Response Surface Method) optimization method. The optimizations were conducted at 1757 rev/min, 45% load. Six factors were considered for the optimization, namely the EGR rate, SOI (Start of Injection), intake boost pressure, and injection pressure, the percentage of fuel in the first injection, and the dwell between injections.

This study is focused on the effect of different valve strategies on the in-cylinder flow and combustion A conventional four-valve pentroof engine was modified to enable optical access to the combustion chamber To get information on the flow, a two-component LDV system was applied The combustion was monitored by the use of cylinder pressure in a one-zone heat release model The results show that the flow in the cylinder with the valves operating in the standard configuration has an expected tumble characteristic In this case the high frequency turbulence is homogeneous and has a peak approximately 20 CAD BTDC With one valve deactivated, the flow shows a swirling pattern The turbulence is then less homogeneous but the level of turbulence is increased When the single inlet valve was phased late against the crankshaft dramatic effects on the flow resulted The late inlet valve opening introduced a low cylinder pressure before the valve opened The high pressure difference across the valve introduced a high-velocity jet into the cylinder Turbulence was increased by a factor of two by this operational mode When two inlet valves were used, a reduction of turbulence resulted from a very late inlet cam phase

2-D LDV measurements were performed on two different cylinder designs in a fired two-stroke engine running with wide-open throttle at 9000 rpm. The cylinders examined were one with open transfer channels and one with cup handle transfer channels. Optical access to the cylinder was achieved by removing the silencer and thereby gain optical access through the exhaust port. No addition of seeding was made, since the fuel droplets were not entirely vaporized as they entered the cylinder and thus served as seeding. Results show that the loop-scavenging effect was poor with open transfer channels, but clearly detectable with cup handle channels. The RMS-value, “turbulence”, was low close to the transfer ports in both cylinders, but increased rapidly in the middle of the cylinder. The seeding density was used to obtain information about the fuel concentration in the cylinder during scavenging.

Auto ignition with SI compression ratio can be achieved by retaining hot residuals, replacing some of the fresh charge. In this experimental work it is achieved by running with a negative valve overlap (NVO) trapping hot residuals. The experimental engine is equipped with a pneumatic valve train making it possible to change valve lift, phasing and duration, as well as running with valve deactivation. This makes it possible to start in SI mode, and then by increasing the NVO, thus raising the initial charge temperature it is possible to investigate the intermediate domain between SI and HCCI. The engine is then running in spark assisted HCCI mode, or spark assisted compression ignition (SACI) mode that is an acronym that describes the combustion on the borderline between SI and HCCI. In this study the effect of changing the in-cylinder flow pattern by increased swirl is studied. This is achieved by deactivating one of the two intake valves.

The effect of in-cylinder flow and turbulence on HCCI operation has been experimentally studied by changing the combustion chamber geometry and the swirl ratio. Four different levels of turbulence were achieved, by altering the swirl ratio both for a high turbulent square bowl-in-piston combustion chamber and for a low turbulent disc combustion chamber. The swirl ratio was altered by using different inlet port designs. The results showed that the combustion chamber geometry plays a large role in HCCI combustion. With the same operating conditions, the combustion duration for the square bowl-in-piston combustion chamber was much longer compared to the disc combustion chamber. On the other hand, a moderate change in swirl ratio proved to have only modest effect on the combustion process. With early combustion timing, the gross indicated efficiency was higher when the square bowl-in-piston combustion chamber.

The main benefit of HCCI engines compared to SI engines is improved fuel economy. The drawback is the diluted combustion with a substantially smaller operating range if not some kind of supercharging is used. The reasons for the higher brake efficiency in HCCI engines can be summarized in lower pumping losses and higher thermodynamic efficiency, due to higher compression ratio and higher ratio of specific heats if air is used as dilution. In the low load operating range, where HCCI today is mainly used, other parameters as friction losses, and cooling losses have a large impact on the achieved brake efficiency. To initiate the auto ignition of the in-cylinder charge a certain temperature and pressure have to be reached for a specific fuel. In an engine with high in-cylinder cooling losses the initial charge temperature before compression has to be higher than on an engine with less heat transfer.

Road transport has become a large source of CO2 emission and accounted in 1998 for about 27% of the CO2 emission in Sweden. Efficient energy use and the use of renewable energy sources are main options for reducing CO2 emission from vehicles in the future. In this study, the use of energy carriers based on renewable energy sources in battery-powered electric vehicles (BPEVs), fuel-cell electric vehicles (FCEVs), hybrid electric vehicles (HEVs) and internal combustion engine vehicles (ICEVs) is compared regarding energy efficiency, emission and cost. The cost calculations include energy, environmental and vehicle costs. The potential for non-technical measures to contribute to a reduction of road transport CO2 emission is also briefly discussed and related to the potential for technical measures. There is the potential to double the primary energy efficiency compared with the current level by utilizing vehicles with electric drivetrains.

A study was performed that takes into account both turbulence and chemical kinetic effects in the numerical simulation of diesel engine combustion in order to better understand the importance of their respective roles at changing operating conditions. An approach was developed which combines the simplicity and low computational and storage requests of the laminar-and-turbulent characteristic-time model with a detailed combustion chemistry model based on well-known simplified mechanisms. Assuming appropriate simplifications such as steady state or equilibrium for most of the radicals and intermediate species, the kinetics of hydrocarbons can be described by means of three overall steps. This approach was integrated in the KIVA-II code. The concept was validated and applied to a single-cylinder, heavy-duty engine. The simulation covers a wide range of operating conditions.

The aim of this study is to see how geometry generated turbulence affects the Rate of Heat Release (ROHR) in an HCCI engine. HCCI combustion is limited in load due to high peak pressures and too fast combustion. If the speed of combustion can be decreased the load range can be extended. Therefore two different combustion chamber geometries were investigated, one with a disc shape and one with a square bowl in piston. The later one provokes squish-generated gas flow into the bowl causing turbulence. The disc shaped combustion chamber was used as a reference case. Combustion duration and ROHR were studied using heat release analysis. A Scania D12 Diesel engine, converted to port injected HCCI with ethanol was used for the experiments. An engine speed of 1200 rpm was applied throughout the tests. The effect of air/fuel ratio and combustion phasing was also studied.

An investigation of high speed direct injection (DI) compression ignition (CI) engine combustion fueled with gasoline (termed GDICI for Gasoline Direct-Injection Compression Ignition) in the low temperature combustion (LTC) regime is presented. As an aid to plan engine experiments at full load (16 bar IMEP, 2500 rev/min), exploration of operating conditions was first performed numerically employing a multi-dimensional CFD code, KIVA-ERC-Chemkin, that features improved sub-models and the Chemkin library. The oxidation chemistry of the fuel was calculated using a reduced mechanism for primary reference fuel combustion. Operation ranges of a light-duty diesel engine operating with GDICI combustion with constraints of combustion efficiency, noise level (pressure rise rate) and emissions were identified as functions of injection timings, exhaust gas recirculation rate and the fuel split ratio of double-pulse injections.

Engine design is a time consuming process in which many costly experimental tests are usually conducted. With increasing prediction ability of engine simulation tools, engine design aided by CFD software is being given more attention by both industry and academia. It is also of much interest to be able to use design information gained from an existing engine design of one size in the design of engines of other sizes to reduce design time and costs. Therefore it is important to study size-scaling relationships for engines over wide range of operating conditions. This paper presents CFD studies conducted for two production diesel engines - a light-duty GM-Fiat engine (0.5L displacement) and a heavy-duty Caterpillar engine (2.5L displacement). Previously developed scaling arguments, including an equal spray penetration scaling model and an extended, equal flame lift-off length scaling model were employed to explore the parametric scaling connections between the two engines.

The objectives of this study were 1) to evaluate the characteristics of rich diesel combustion near the stoichiometric operating condition, 2) to explore the possibility of stoichiometric operation of a diesel engine in order to allow use of a three-way exhaust after-treatment catalyst, and 3) to achieve practical operation ranges with acceptable fuel economy impacts. Boost pressure, EGR rate, intake air temperature, fuel mass injected, and injection timing variations were investigated to evaluate diesel stoichiometric combustion characteristics in a single-cylinder high-speed direct injection (HSDI) diesel engine. Stoichiometric operation in the Premixed Charge Compression Ignition (PCCI) combustion regime and standard diesel combustion were examined to investigate the characteristics of rich combustion. The results indicate that diesel stoichiometric operation can be achieved with minor fuel economy and soot impact.