High-speed Direct-injection Engine Research Articles

Combustion and soot formation characteristics of homogeneous supercritical sprays of dieseline blend in constant volume chamber

In present work, combustion and soot formation characteristics of supercritical (SC) sprays are studied in a cylindrical constant volume combustion chamber under diesel engine-like experimental conditions. Hot surface temperature range (673 K to 723 K), initial cylinder pressure range (2 MPa to 4 MPa) and injection pressure range of 10 MPa to 30 MPa are the experimental conditions. Photo sensor and piezoelectric sensors are employed for indicating combustion and injection events respectively. Commercial diesel fuel and dieseline blend are employed for analyzing combustion of normal diesel and SC sprays respectively. It is investigated that duration of combustion of SC sprays are substantially lower than normal diesel sprays at all experimental conditions. Percentage reduction in DOC of SC sprays as compared to diesel sprays is above 35% for all cases. Percentage reduction in DOC of SC sprays is observed highest at higher IP of 30 MPa. Percentage reduction in soot formation (SF) in SC spray combustion is more than 90% at all operating conditions. At normal diesel engine operating conditions, nearly 82% reduction in DOC and about 96% reduction in SF are found. Combustion of SC sprays seems hot air and single-phase homogeneous combustion unlike that of normal diesel sprays having hot surface ignition/combustion. SC spray injection system proves out to be a faster as well as cleaner combustion technology for future high speed direct-injection engines.

A computational analysis of the impact of bore-to-stroke ratio on emissions and efficiency of a HSDI engine

Research on combustion systems for Internal Combustion Engines (ICE) is guided by the necessity of improving engine efficiency while achieving the pollutant regulations. In this framework, this study identifies and describes the effect of the bore-to-stroke ratio (B/S) on the combustion system performance and emissions by means of computational fluid dynamics (CFD).The study is applied to a 4-cylinder 4-stroke High Speed Direct Injection (HSDI) CI engine. It is divided in two parts, the first part is focused on one operating point and presents a detailed description of the main effects of different B/S ratios configurations, and the second part compares the results with different engine operating conditions. For both parts the air management, injection settings and compression ratio were kept constant in order to isolate the impact of the B/S ratio.The results confirmed that the indicated thermal efficiency was increased for lower B/S ratio because of the combustion chamber surface area decrease and faster combustion. Regarding the emissions, NOx and soot presented a strong and opposed dependence on B/S ratio generated mostly due to enhanced air–fuel mixing for lower B/S ratio. Finally, those trends were proven to be independent from the operating condition, giving the study a more general value.

Study on LTC for light duty engines – Part 2 – Spray enhancements

This paper presents the 2nd part of a study on low temperature diffusive combustion in a small HSDI (High Speed Direct Injection) engine with the objective of avoiding simultaneously NOX and soot formation, aiming to extend the range of operation conditions where this combustion strategy has been achieved and. Also, it was intended to reduce CO and HC emissions, considered very high in the 1st part of the tests. New hardware configuration was chosen in order to improve air entrainment in the lift-off length such as increasing injection pressure, reducing fuel injection rate and nozzle hole diameter. Also, a parametric study on the behavior of in-cylinder air thermodynamic characteristics towards the diffusion-flame low temperature combustion was also carried out in order to evaluate the important aspects of each one and observe how the LTC range has been extended.The strategy is based mainly in a significant reduction of the equivalence ratio at the lift-off length cross section and the combustion temperature, maintaining the conventional mixing controlled diesel jet structure. In this 2nd part of the study, injection pressure was increased and new nozzles with reduced holes were used to enhance air entrainment and the injection rate was reduced to extend the duration of diffusion-flame combustion phase.The new proposal allowed extending Diffusion-flame LTC range, being possible to achieve this combustion modality with higher air temperature which lead to considerable reduction in HC, CO and combustion noise while NOx and Soot remained insignificant.

Combustion and Emissions in an HSDI Engine Running on Diesel or Vegetable Oil Base Fuel with n-Butanol or Diethyl Ether As a Fuel Extender

AbstractThe present investigation compares the combustion, performance, and exhaust emissions of diesel fuel in blends with either 24% n-butanol or 24% diethyl ether (DEE), and of vegetable (cottonseed) oil in blends with either 20% n-butanol or 20% diethyl ether, fueling a standard, experimental, single-cylinder, four-stroke, high-speed direct injection (HSDI), Hydra diesel engine operated at three different loads. Fuel consumption, and exhaust smoke, nitrogen oxides (NOx), carbon monoxide (CO), and total unburned hydrocarbons (HC) were measured. The differences in combustion, performance, and exhaust emissions of those biofuel blends are compared from the baseline operations, i.e., when working with the neat base fuels (diesel fuel or vegetable oil). Fuel injection, combustion chamber pressure, heat release rate, and temperature diagrams, reveal interesting features of the combustion mechanisms. These results and the differing physical and chemical properties of those biofuels are used to aid the interp...

Optical investigation of fuel and in-cylinder air-swirl effects in a high-speed direct-injection engine

The primary aim of this study is to investigate current issues of combustion in high-speed direct-injection diesel engines in detail by optical diagnostics. Both fuel and engine design are considered. Recently, measurements of engine-out emissions demonstrated that approximately soot-free combustion can be achieved using a newly designed two-component fuel named BLT. It was composed of 70% butyl levulinate and 30% n-tetradecane (by volume). In this work, the underlying mechanism is clarified by in-cylinder visualization of OH* radicals and soot. In particular, it turns out that in-cylinder soot formation is avoided almost completely, that is, the soot oxidation process is much less important. This is basically achieved by both the oxygen content (about 21%) and the low cetane number (approximately 33) of BLT. The latter leads to enhanced pre-mixing of fuel and air. Consequently, soot formation can be greatly reduced because it depends on the air–fuel ratio of the mixture shortly before high-temperature combustion. The influence of in-cylinder air swirl on combustion and soot formation is also studied for both BLT and conventional diesel fuel, respectively, using the same optical diagnostic. The measurements show that the combustion zone strongly depends on the local gas-flow velocity for diesel fuel. Soot formation decreases with increasing swirl because of enhanced air entrainment and pre-mixing of fuel and air. In addition, the results indicate that soot oxidation is improved under high-swirl conditions for diesel fuel. In contrast, the influence of swirl on the combustion of BLT is overall found to be weak, suggesting that swirl could be reduced in future high-speed direct-injection engines for BLT-like fuels.

Effects of injection parameters and EGR on exhaust soot particle number-size distribution for diesel and RME fuels in HSDI engines

The exhaust soot particles number size distributions obtained from the combustion of diesel and RME fuels were investigated in a high speed direct injection (HSDI) diesel engine for different engine operating conditions viz., fuel injection pressure, injection timing, exhaust gas recirculation (EGR) and engine load. An Electrostatic Mobility Spectrometer (EMS) was used for characterising the exhaust soot particle number size distribution. Increasing the fuel injection pressure reduced the particle size and its number concentration in the accumulation mode under low and high load conditions, but an opposite trend was observed to the particle number concentration in the nucleation mode under higher load operation. The effect of fuel injection timings on the particle number concentration was not clear and consistent between diesel and RME fuels under low load operation. Under high load operation, the overall particle number concentration for RME decreased but for diesel only the nucleation mode decreased, while the accumulation mode remained unaltered when the fuel injection timing was retarded. The addition of EGR caused the particles to agglomerate and form larger size particles, which were observed mostly in the accumulation mode. Under most of the engine operating conditions RME emitted lower soot particle concentration than diesel under both nucleation and accumulation modes. The presence of oxygen in the fuel has the potential to lower the exhaust particle number concentration in diesel engines.

Chemical Characteristics of the Soot Produced in a High-Speed Direct Injection Engine Operated with Diesel/Biodiesel Blends

The aim of this work is to study the influence of the molecular structure of fatty acid esters present in biodiesel and their blends with diesel on the chemical characteristics of the emitted particulate matter. Biodiesel produced from palm oil, jatropha, castor oil and sachainchi was blended at 5% and 20% by volume with diesel. These fuels were used for the operation of a four-cylinder direct injection automotive diesel engine. The equivalent ratio was kept between 0.36 and 0.40, and the engine was operated at the point of minimum air–fuel ratio and maximum smoke opacity. The amount of particulate matter emitted was evaluated by opacity index. A marked reduction in soot formation was observed when the concentration of unsaturated methyl esters in the fuel was at low concentrations. This was accompanied by a reduction of the aliphatic carbon content in the particulate matter.

On the combination of high-pressure and low-pressure exhaust gas recirculation loops for improved fuel economy and reduced emissions in high-speed direct-injection engines

In this paper, an experimental study of the combination of low-pressure and high-pressure exhaust gas recirculation architectures has been carried out. In the first part of the paper, the effects of both high-pressure and low-pressure exhaust gas recirculation architectures on engine behaviour and performance are analysed by means of a series of steady tests. In the second part, the effects of the combination of both architectures are addressed. The results show that the low-pressure configuration improves high-pressure exhaust gas recirculation results in brake-specific fuel consumption, nitrogen oxides and exhaust gas opacity; nevertheless, hydrocarbon emissions are increased, especially during the engine warm up. In addition, the exhaust gas recirculation rate achieved with low-pressure systems is limited by the pressure difference between diesel particulate matter outlet and compressor inlet; therefore, the high-pressure system can be used to achieve the required exhaust gas recirculation levels without increasing pumping losses. In this sense, the combination of both exhaust gas recirculation layouts offers significant advantages to reduce emissions and fuel consumption to meet future emission requirements.

Experimental Investigation of Thermal Load in High Speed Direct Injection Diesel Engine Under the Control of Various Engine Performance Parameters

Multiple injection strategies are being widely utilized to reduce the vibration, noise, and particle emission in diesel engines. A considerable amount of research related to attempts to increase the maximum power and to reduce vibration, noise, and particulate matters has been done. However, investigations of various performance parameters in terms of the thermal load in high speed direct injection engines are rarely to be found despite the fact that the relationship between these parameters and the reliability of the engine is important for mass production. Hence, the thermal load imposed on the cylinder head and cylinder block of a four-cylinder diesel engine was investigated under the most severe test conditions, at the rated speed and with a full load, by changing the performance parameters such as the main injection timing, the fuel pressure in the common rail, the boost pressure, the exhaust gas recirculation, the fuel quantity of the pilot injection, the timing of the pilot injection, the fuel quantity of the postinjection, and the timing of postinjection. Experimental results showed that the main injection timing among other parameters was the parameter that influenced the thermal load most at the rated engine speed and under a full load condition.

Assessment of large-eddy simulation feasibility in modelling the unsteady diesel fuel injection and mixing in a highspeed direct-injection engine

This paper aims to assess the feasibility of largeeddy simulation LES as applied to a real engine configuration. Two cases of LES were performed together with a reference Reynoldsaveraged NavierStokes RANS simulation to study their performances in the prediction of the fuel injection and mixing in a highspeed directinjection diesel engine. In addition, sensitivity of the LES results with respect to mesh resolution was investigated, as LES requires a higher mesh density and the filtering process depends on the mesh size. The LES meant that detailed information could be obtained on the fuel spray development and turbulent flow field that was not possible to capture using the RANS modelling approach. It was found that the LES captures flow structures that have a pronounced impact on the prediction of the fuel injection and mixing. Highresolution LES predicted higher liquid and vapour penetration into the cylinder, which is in better agreement with the experimental data obtained at Delphi Diesel Systems than is the RANS prediction. It was also shown that using a finer mesh in LES yields improvements in turbulent flow field prediction, at the same time reducing contribution of the modelled part of the turbulent kinetic energy. Overall, it was proved that LES is a superior alternative to the traditional RANS approach for turbulent twophase flows encountered in diesel fuel injections where flow unsteadiness is prominent. Improved predictions obtained from an advanced LES can subsequently enhance the understanding of the fuel injection process and assist the engine experimentation and design.

Comprehensive study of biodiesel fuel for HSDI engines in conventional and low temperature combustion conditions

In this research, an experimental investigation has been performed to give insight into the potential of biodiesel as an alternative fuel for High Speed Direct Injection (HSDI) diesel engines. The scope of this work has been broadened by comparing the combustion characteristics of diesel and biodiesel fuels in a wide range of engine loads and EGR conditions, including the high EGR rates expected for future diesel engines operating in the low temperature combustion (LTC) regime. The experimental work has been carried out in a single-cylinder engine running alternatively with diesel and biodiesel fuels. Conventional diesel fuel and neat biodiesel have been compared in terms of their combustion performance through a new methodology designed for isolating the actual effects of each fuel on diesel combustion, aside from their intrinsic differences in chemical composition. The analysis of the results has been sequentially divided into two progressive and complementary steps. Initially, the overall combustion performance of each fuel has been critically evaluated based on a set of parameters used as tracers of the combustion quality, such as the combustion duration or the indicated efficiency. With the knowledge obtained from this previous overview, the analysis focuses on the detailed influence of biodiesel on the different diesel combustion stages known ignition delay, premixed combustion and mixing controlled combustion, considering also the impact on CO and UHC pollutant emissions. The results of this research explain why the biodiesel fuel accelerates the diesel combustion process in all engine loads and EGR rates, even in those corresponding with LTC conditions, increasing its possibilities as alternative fuel for future DI diesel engines.

Modelling for investigation of combustion and emission characteristics in a high-speed direct-injection diesel engine with light duty under various operating conditions

A numerical study was conducted to investigate combustion and emission characteristics in a high-speed direct-injection engine with a common-rail injection system under various operating conditions. In order to analyse the combustion characteristics, several models were used in this study. They were the renormalization group k– ε model, the hybrid Kelvin—Helmholtz (wave) and the Rayleigh—Taylor model, the shell auto-ignition model, and the laminar and turbulent characteristic timescale combustion model. The prediction of exhaust emissions was conducted using nitrogen oxide NO x formation with an extended Zel'dovich mechanism and Hiroyasu soot formation with the Nagle—Strickland-Constable oxidation model respectively. Experimental combustion and emission characteristics were compared with calculated results under various operating conditions, such as injection timing, injection pressure, fuel mass, and engine speed. The calculated results show similar patterns to the experimental results in the cylinder pressure and the rate of heat release. In the emissions characteristics, NO x emission decreased as injection timing was retarded and the NO x and soot amounts increased with the increase in the injected fuel mass. The calculated soot trends for various injection timings showed different patterns from the experimental trends as the injection timing were retarded.

An experimental study of the dual-fuel performance of a small compression ignition diesel engine operating with three gaseous fuels

A dual-fuel engine is a compression ignition (CI) engine where the primary gaseous fuel source is premixed with air as it enters the combustion chamber. This homogenous mixture is ignited by a small quantity of diesel, the ‘pilot’, that is injected towards the end of the compression stroke. In the present study, a direct-injection CI engine, was fuelled with three different gaseous fuels: methane, propane, and butane. The engine performance at various gaseous concentrations was recorded at 1500 r/min and quarter, half, and three-quarters relative to full a load of 18.7 kW. In order to investigate the combustion performance, a novel three-zone heat release rate analysis was applied to the data. The resulting heat release rate data are used to aid understanding of the performance characteristics of the engine in dual-fuel mode. Data are presented for the heat release rates, effects of engine load and speed, brake specific energy consumption of the engine, and combustion phasing of the three different primary gaseous fuels. Methane permitted the maximum energy substitution, relative to diesel, and yielded the most significant reductions in CO2. However, propane also had significant reductions in CO2 but had an increased diffusional combustion stage which may lend itself to the modern high-speed direct-injection engine.

The use of micro-orifice nozzles and swirl in a small HSDI engine operating at a late split-injection LTC regime

This paper describes the investigation of low-temperature combustion (LTC) in a small single-cylinder research high-speed direct injection (HSDI) diesel engine. This engine is representative of passenger car turbocharged diesel engines equipped with a particulate trap and an oxidation catalyst. A medium-load operation mode has been evaluated where the diesel fuel is injected in two injection events close to top dead centre, and high levels of exhaust gas recirculation are used (near stoichiometric air-fuel ratios). The combustion is characterized by extremely low emission of nitrogen oxides (of the order of 10–15 parts per million) and low combustion noise. Three injector nozzles have been tested with 6, 12, and 18 orifices. The orifice diameters are in the range 70–120 μM and have been chosen to obtain injector nozzles with the same hydraulic flow. All three nozzles have been tested at a condition without swirl and at a mean swirl number of 1.7. The effects of the nozzle orifice number and swirl have been investigated by means of analysis of fuel spray, combustion, and emissions. It was found that when the number of orifices is increased, the rate of heat release during the first half of combustion is enhanced. However, during the second part of the combustion, interactions between sprays worsen the air-fuel mixing process and reduce the rate of heat release. Swirl was found to amplify the effects of spray interactions. While normally swirl speeds up the combustion in the second half of the combustion, the opposite happens when spray-spray interaction occurs.

Computational fluid dynamics study of the effects of the re-entrant lip shape and toroidal radii of piston bowl on a high-speed direct-injection diesel engine's performance and emissions

The piston bowl design is one of the most important factors that affect the air-fuel mixing and the subsequent combustion and pollutant formation processes in a direct-injection diesel engine. The bowl geometry and dimensions, such as the pip region, bowl lip area, and toroidal radius, are all known to have an effect on the in-cylinder mixing and combustion process. In order to understand better the effect of re-entrant geometry, three piston bowls with different toroidal radii and lip shapes were investigated using computational fluid dynamics engine modelling. KIVA3V with improved submodels was used to model the in-cylinder flows and combustion process, and it was validated on a high-speed direct-injection engine with a second-generation common-rail fuel injection system. The engine's performance, in-cylinder flow, and combustion, and emission characteristics were analysed at maximum power and maximum torque conditions and at part-load operating conditions. Three injector protrusions and injection timings were investigated at full-load and part-load conditions.

Modelling of turbocharged diesel engines in transient operation. Part 2: Wave action models for calculating the transient operation in a high speed direct injection engine

Part 1 of this paper analysed the physical phenomena involved in the transient operation of turbocharged diesel engines, together with the principles of diesel combustion characterization during the transient process. This second part describes a calculation model developed to predict engine transient performance based on an existing wave action code. Relevant improvements introduced are combustion process simulation and modelling of heat transfer, variable geometry turbine behaviour and mechanical losses. Experimental load transient tests with a high speed direct injection engine have been performed, with the aim of assessing the model accuracy. The main evaluation parameters were instantaneous variation during turbocharger rotating speed transient, boost pressure, air mass flow, injected fuel and exhaust pressures.

Meeting the Challenge of Low Emissions and Fuel Economy with the Ricardo Four-Valve High-Speed Direct Injection Engine

In order to investigate and demonstrate the potential of the high-speed direct injection (HSDI) diesel engine, Ricardo have undertaken a programme of research and analysis into the performance and emissions of a four-valve/cylinder combustion system. Analytical studies were based on a computational fluid dynamics investigation to model in-bowl events of fuel spray/air interactions and to improve understanding of the mixing processes. The major variables studied during the test programme included swirl ratio, combustion bowl geometry, nozzle configuration, contemporary and advanced electronic rotary fuel injection pumps and the effects of exhaust gas recirculation (EGR). A systematic optimization programme provided a fixed swirl configuration capable of achieving in excess of 15 bar b.m.e.p. (brake mean effective pressure) while providing less than 1.0 Bosch smoke unit. R49 EURO II NOx levels were met with competitive smoke, particulate emissions and fuel economy, demonstrating excellent potential for full EURO II compliance with further development. Vehicle emissions and fuel consumption simulations have shown that the combustion system has the potential to meet both the heavy and light duty emissions legislation planned for the 1990s.

Combustion in a Direct Injection Diesel Engine with Increased Clearance Volume

The aim of the investigation was to analyse the effects of an increased clearance volume on the performance of a high-speed direct injection (DI) diesel engine, and to seek ways of ameliorating problems with combustion. Tests were carried out on a high-speed DI engine at the standard and at a lower compression ratio, and the problems with combustion were analysed. Modifications made to the fuel injection system and engine operating conditions at the lower compression ratio resulted in substantial improvements in power output and fuel economy. This investigation is relevant to DI diesel engines operating with variable compression ratio.

A High-Speed Direct Injection Diesel Engine for Passenger Cars

The paper describes the development of a high-speed direct injection (HSDI) diesel engine suitable for passenger car applications. The evolution from a low emissions medium-speed engine, through a four-cylinder 2.3 litre research engine, into a four-cylinder 2.0 litre production engine is presented. The challenge to the engineer has been to develop the HSDI engine to operate with acceptable noise, emissions, smoke and driveability over the wide speed range (up to 5000 r/min) required for passenger cars. The key element in this task was the optimization of the combustion system and fuel injection equipment. The HSDI is shown to have a significant fuel economy advantage over the prechamber indirect injection (IDI) engine. Future developments of the fuel injection system are described which will further enhance the HSDI engine and provide additional noise and emissions control.

The Ford 2.5 Litre Direct Injection Naturally Aspirated Diesel Engine

The advantages of a high-speed direct injection diesel over an indirect injection engine are well established. In the last decade many studies have been presented which suggest that most of the technical issues preventing operation at high speed have been overcome. The new Ford 2.5 litre engine introduces a first generation of production high-speed direct injection engines. Based on controlled high swirl air management, combined with high rates of fuel injection, the engine produces 52 kW at 4000 r/min. Initial installation of the 2.5 litre high-speed direct injection engine is in the Ford Transit range of vehicles where 25 per cent fuel economy improvements over its predecessor, the York 2.36 litre indirect injection engine, have been achieved. Designed to meet the demands of modern vehicle application, the engine includes many features to improve reliability and durability. This paper describes the engine systems and components of the engine, together with the key aspects of the performance development with specific reference to the actions employed to control noise.