Increased efficiency through gasoline engine downsizing

CONTENTS: Introduction; Technologies for Downsizing; Low-Speed Pre-Ignition; LSPI Mechanisms; Research; Conclusion

Total pressure loss mechanism of centrifugal compressors

This paper describes the construction of the centrifugal compressor model and its validation with the experimental data. The compressor model in this paper uses One-dimensional (1D) thermo-fluid equations to analyse the compressor side of a turbocharger. Under a specified set of turbocharger geometry, atmospheric conditions, rotational speed, and fluid mass flow rate, the model can calculates the static and total temperatures, velocities, static and total pressures, pressure losses, and isentropic efficiencies for each compressor component. Instead of using lumped loss parameters, the compressor model includes established loss models found in the open literature. Not only in the impeller, the losses in the diffuser and the volute are modelled. With the model, it is possible for a parametric study on the effect of each loss mechanism on the performance, and which can aid the designer in justifying design decisions minimising the magnitude of the losses and thus positively influence the overall performance. The compressor model can also be applied to investigate the two stage Turbocharging or Variable Geometry Turbocharger (VGT) in the future

A simulation study on the effect of inlet valve opening on performance of high speed engines

Variable camshaft phasing (VCP) system is a potential valvetrain technology for high speed engine applications since it does not increase the effective valve dynamic mass, which is essential to high speed operation. In addition, it is a relatively simple and low cost system. Inlet Valve Opening (IVO) is the start of valve overlap. It has significant effect on engine breathing. As part of a general assessment on the VCP system, such an effect was calculated and analysed using a zero- and one- dimensional based commercial engine simulation package, Lotus Engineering Simulation (LES) and reported in this paper. The simulation was based on a 0.6l, 4-cylinder, 4-stroke, high speed (up to 13500rpm), production spark ignition engine. It was found that IVO can either improve the utilisation of inlet charging effect or reduce backflow during the valve overlap period caused by speed related wave effects from the exhaust manifold

Modelling of transient stretched laminar flame speed of hydrogen-air mixtures using combustion kinetics

The calculations of laminar burning velocity are mostly based on empirical correlations obtained from combustion bomb experiments. There is a noticeable scarcity of the fitting parameters in these correlations, especially under increased temperature and pressure conditions. The effects of flame stretch and instabilities further complicate the situation as these effects are not distinguished in some correlations. Furthermore, although combustion products are of great interests in recent computer simulations of combustion, it is difficult to integrate combustion chemistry into the existing correlations. This paper discusses a laminar burning velocity model for hydrogen-air mixtures in a constant volume combustion bomb. The model is based on a one-dimensional three-zone thermodynamic model that calculates the mass transfer and diffusion and the heat transfer between zones. The chemical process involved in the combustion is solved by an in-house chemical kinetics solver with an established reduced hydrogen-oxidation mechanism from literature. The effects of flame stretch and instabilities are simulated using existing experimental data. The calculated laminar burning velocities are compared to existing empirical correlations and experimental data obtained from constant volume combustion bomb tests. The model is able to simulate laminar burning velocities and have the potential to be integrated into IC engine models in the future

A review of experimental and simulation studies on controlled auto-ignition combustion

Engines with controlled auto-ignition (CAI) combustion offer a number of benefits over conventional spark ignited (SI) and compression ignited (CI) engines, such as much lower NOx emission due to its relatively low combustion temperature, negligible cycle-to-cycle variation due to its self-ignition nature, higher combustion efficiency at part load than its SI counterpart, and low soot emissions since a homogeneous lean air/fuel mixture is being employed. Unlike conventional SI and CI engines, where combustion is directly controlled by the engine management system, the combustion in CAI engines is controlled by chemical kinetics only. Over the past two decades, a number of technologies have been developed to initiate such combustion on both 2 and 4-stroke engines with various fuels, but none of them could maintain the combustion over the wide engine operation range. Remaining problems include control of ignition timing and the heat release rate over the entire engine operation range. This paper reviews some of the engine research results and available data from combustion kinetics studies. It has been observed that the quality of engine charge affects both ignition timing and the heat release rate of CAI combustion, but a certain charge temperature is essential to start the ignition of CAI combustion

Thermodynamic study on the solubility of NaBH4 and NaBO 2 in NaOH solutions

Extensive research has been performed for on-board hydrogen generation, such as pyrolysis of metal hydrides (e.g. LiH, MgH2), hydrogen storages in adsorption materials (e.g. carbon nanotubes and graphites), compressed hydrogen tanks and the hydrolysis of chemical hydrides. Among these methods, the hydrolysis of NaBH4 has attracted great attention due to the high stability of its alkaline solution and the relatively high energy density, with further advantages such as moderate temperature range (from -5°C to 100°C) requirement, non-flammable, no side reactions or other volatile products, high purity H2 output. The H2 energy density contained by the system is fully depend on the solubility of the complicated solution contains reactant, product and the solution stabiliser. In this work, an approach based on thermodynamic equilibrium was proposed to model the relationship between the solubility of an electrolyte and temperature, and the effect of another component on its solubility. The relationship was then applied to NaBH4 and NaBO2 aqueous solutions, and the effect of introduction of NaOH on their solubility after deriving their solubility from phase diagrams. The data has been shown in good agreement with the proposed model. © Copyright 2011 Society of Automotive Engineers of Japan, Inc. and SAE International

An investigation into the use of fluidic devices as gas fuel injectors for natural gas engines

A novel gas fuel injector system based on the use of monostable fluidic devices is described in this paper. The proposed system consists of non-moving-part fluidic devices which are capable of operating in a Pulse Width Modulated (PWM) control mode and of handling a large amount of gas flow for engine operations. The system also includes an electro-fluidic interface for fluidic switching and air-gas mixing nozzles for better mixing quality. Two prototype fluidic injector units were produced and their steady-state and dynamic characteristics were evaluated on a laboratory test rig. The results were compared with those from several commercial gas injectors and it was found that the fluidic injector has a faster dynamic response and a smaller cycle-cycle variations

Modelling of transient stretched laminar flame speed of hydrogen-air mixtures using combustion kinetics

The calculations of laminar burning velocity are mostly based on empirical correlations obtained from combustion bomb experiments. There is a noticeable scarcity of the fitting parameters in these correlations, especially under increased temperature and pressure conditions. The effects of flame stretch and instabilities further complicate the situation as these effects are not distinguished in some correlations. Furthermore, although combustion products are of great interests in recent computer simulations of combustion, it is difficult to integrate combustion chemistry into the existing correlations. This paper discusses a laminar burning velocity model for hydrogen-air mixtures in a constant volume combustion bomb. The model is based on a one-dimensional three-zone thermodynamic model that calculates the mass transfer and diffusion and the heat transfer between zones. The chemical process involved in the combustion is solved by an in-house chemical kinetics solver with an established reduced hydrogen-oxidation mechanism from literature. The effects of flame stretch and instabilities are simulated using existing experimental data. The calculated laminar burning velocities are compared to existing empirical correlations and experimental data obtained from constant volume combustion bomb tests. The model is able to simulate laminar burning velocities and have the potential to be integrated into IC engine models in the future

A zero-dimensional combustion model with reduced kinetics for SI engine knock simulation

High load performance and fuel economy of gasoline engines are limited by knocks. Such limitations are becoming worse when the engine is heavily super-charged for high BMEP outputs. Spark ignition timing retardation has been an efficient method to avoid the knock but results in reduced engine performance and poor fuel economy. A better understanding of knock, which could be used to optimize the engine design, ignition timing optimization in particular, is important. In this research, a simulation model for SI engine knock has been developed. The model is based on a three-zone approach (unburned, burning and burned zones). The Tanaka’s reduced chemical kinetic model for a commercial gasoline fuel with an RON of 95 has been modified and applied in both burned and unburned zones incorporated with the LUCKS (Loughborough University Chemical Kinetics Simulation) code. Both post-flame heat release and pre-flame autoignition have be simulated. The burning zone uses equilibrium combustion thermodynamic models. The simulated results have been validated against experimental results, and good agreements have been achieved

Experimental study on a small diesel genset dual fuelled with methane

A dual fuel engine is an internal combustion engine where the primary gaseous fuel source is ignited by a small quantity of diesel known as the ‘pilot’ that is injected towards the end of the compression stroke. The motivation to dual-fuel a CI engine is partly economic due to the lower cost of the primary fuel, and partly environmental as some emissions characteristics are improved. In this study, a direct injection four cylinder CI engine, typically used in engine-generator set or genset applications, was fuelled with methane. The performance and emissions (NOx and smoke) characteristics of various gaseous concentrations were recorded at 1500rpm (synchronous speed) and at no load, ¼, ½, ¾ and full load. In order to investigate the combustion performance under these different conditions, a three zone heat release rate analysis was applied to the data. The resulting mass burned rate, ignition delay and combustion duration are used to explain the emissions and performance characteristics of the engine. The results of the study showed that the combined effect of dual fuelling a DI engine with methane reduces both NOx and smoke emissions. This technology provided a beneficial method to manipulate the classic diesel engine NOx-smoke tradeoff