Influence of the variable valve timing strategy on the control of a homogeneous charge compression (HCCI) engine

Homogeneous Charge Compression Ignition (HCCI) engine concept has the potential to be high efficient and to produce low NOx and particulate matter emissions. However, the problem of controlling the combustion over the entire load/speed range limits its practical application. The HCCI combustion is controlled by chemical kinetics of the charge mixture, with no influence of the flame diffusion or turbulent propagation. Therefore, to achieve a successful control of the HCCI process, the composition, temperature and pressure of the charge mixture at IVC point have to be controlled. The use of the variable valve timing strategy that enables quick changes in the amount of trapped hot exhaust gases shows the potential for the control of the HCCI combustion. The aim of this paper is to analyse influence of the variable valve timing strategy on the gas exchange process, the process between the first valve open event (EVO) and the last valve closing event (IVC), in a HCCI engine fuelled with standard gasoline fuel (95RON). The gas exchange process affects the engine parameters and charge properties and therefore plays a crucial role in determining the control of the HCCI process. Analysis is performed by the experimental and modelling approaches. The single-cylinder research engine equipped with the fully variable valve train (FVVT) system was used for the experimental study. A combined code consisting of a detailed chemical kinetics code and one-dimensional fluid dynamics code was used for the modelling study. The results obtained indicate that the variable valve timing strategy has a strong influence on the gas exchange process, which in turn influences the engine parameters and the cylinder charge properties, hence the control of the HCCI process. The EVC timing has the strongest effect followed by the IVO timing, while the EVO and IVC timings have the minor effects

The thermal effect of internal exhaust gas recirculation on controlled auto ignition

Controlled Auto Ignition (CAI) uses compression heat to auto ignite a homogeneous air/fuel mixture. Using internal exhaust gas recirculation (IEGR) as an indirect control method, CAI offers superior fuel economy and pollutant emission reductions. Practically, this can readily be achieved by a method of early exhaust valve closure and late inlet valve opening to trap exhaust gas residuals within the cylinder from one cycle to the next. In order to understand the combustion mechanism, we did a comprehensive investigation on CAI fuelled with isooctane. Test data was gathered from a single cylinder research engine equipped with Lotus’ Research Active Valve Train (AVT) System, and the modelling study was based on detailed chemical kinetics. It was found that CAI can only occur when the thermal energy of the engine charge, which is a mixture of air / fuel and IEGR, reaches a certain level. This thermal energy is inherited from IEGR trapped inside the cylinder from the previous combustion cycle, when the air / fuel fresh charge was supplied at ambient conditions

An investigation of using various diesel-type fuels in homogeneous charge compression ignition engines and their effects on operational and controlling issues

Homogeneous charge compression ignition (HCCI) engines appear to be a future alternative to diesel and spark-ignited engines. The HCCI engine has the potential to deliver high efficiency and very low NOx and particulate matter emissions. There are, however, problems with the control of ignition and heat release range over the entire load and speed range which limits the practical application of this technology. The aim of this paper is to analyse the use of different types of diesel fuels in an HCCI engine and hence to find the most suitable with respect to operational and control issues. The single-zone combustion model with convective heat transfer loss is used to simulate the HCCI engine environment. n-Heptane, dimethyl ether and bio-diesel (methyl butanoate and methyl formate) fuels are investigated. Methyl butanoate and methyl formate represent surrogates of heavy and light bio-diesel fuel respectively. The effects of different engine parameters such as equivalence ratio and engine speed on the ignition timing are investigated. The use of internal exhaust gas recirculation is investigated as a potential strategy for controlling the ignition timing. The results indicate that the use of bio-diesel fuels will result in lower sensitivity of ignition timing to changes in operational parameters and in a better control of the ignition process when compared with the use of n-heptane and dimethyl ether

Enlarging the operational range of a gasoline HCCI engine by controlling the coolant temperature

The Homogeneous Charge Compression Ignition (HCCI) engine combustion uses heat energy from trapped exhaust gases enhanced by the piston compression heating to auto ignite a premixed air/gasoline mixture. As the HCCI combustion is controlled by the charge temperature, composition and pressure, it therefore, prevents the use of a direct control mechanism such as in the spark and diesel combustion. Using a large amount of trapped residual gas (TRG), is seen as one of the ways to achieve and control HCCI in a certain operating range. By varying the amount of TRG in the fresh air/fuel mixture (inside the cylinder), the charge mixture temperature, composition and pressure can be controlled and hence, the auto ignition timing and heat release rate. The controlled auto ignition (HCCI) engine concept has the potential to be highly efficient and to produce low NOx, carbon dioxide and particulate matter emissions. It has however been found that the TRG promoted HCCI combustion mainly depends on the quantity and quality of TRG, that on the other hand depend on the combustion quality of the previous cycle, valve timing, engine load and speed. In that way, the operating range in terms of engine load and speed, for a naturally aspirated HCCI engine, is restricted by a misfire at low load and by fierce (knocking) combustion at high load. One possible approach to extend the operating range of the HCCI combustion is to influence quality of the TRG by adjusting the coolant temperature. The engine coolant temperature influences the in-cylinder heat transfer process, which in turn influences the charge mixture temperature and therefore the HCCI combustion process itself. The aim of this paper is to present tests and results obtained on the single cylinder research engine, equipped with a Fully Variable Valve Train (FVVT) run over a range of coolant temperature in the HCCI combustion mode and fuelled with gasoline fuel. The results obtained suggest that with reducing the coolant temperature, the high load limit can be extended up to 14%, while with increasing the coolant temperature the low load limit can be extended up to 28%

An automotive engine charge-air intake conditioner system: analysis of fuel economy benefits in a gasoline engine application

A combination of analytical techniques has been used to quantify the potential fuel economy benefits of an automotive engine charge-air intake conditioner system applied to a spark-ignited gasoline engine. This system employs a compressor, intercooler, and expander to provide increased charge density with the possibility of reducing charge-air temperature below sink temperature. This reduction in charge-air temperature provides the potential for improved knock resistance at full load; thereby allowing the possibility of increasing compression ratio with corresponding benefits in thermodynamic cycle efficiency and part-load fuel economy. The four linked and interfaced models comprised a first-law thermodynamic model of the charge-air conditioner system, a one-dimensional engine cycle simulation, a two-zone combustion model, and a knock criterion model. An analysis was carried out under full load at 3000 r/min and showed that a charge-air conditioner system - with compressor, intercooler, and expander efficiencies of 0.8 - allowed the compression ratio to be increased by approximately half a ratio, which gave up to 1.5 per cent reduction in brake specific fuel consumption at 2000 r/min 2 bar brake mean effective pressure when compared with a conventional pressure charger intercooler system with no expander

An automotive engine charge-air intake conditioner system: thermodynamic analysis of performance characteristics

A first law thermodynamic model has been developed and used to characterize the performance of an automotive engine charge-air intake conditioner system. This system employs a compressor, intercooler, and expander to provide increased charge density with the possibility of reducing, the charge-air temperature below the sink temperature. The model was validated against experimental measurements. The variation of system effectiveness with compressor, intercooler, and expander efficiency was quantified and system operating limits were identified. While the expander was found to have a greater effect than the compressor, the performance of the system was shown to be most dependent upon intercooler effectiveness

The advance combustion control in a hybrid SI/HCCI engine by using ion current sensing

In a future ‘hybrid mode’ SI/HCCI engine transition between these modes, over the operating map, will play a crucial role. The engine management system must provide a fast and smooth transition between these two modes, hence a new combustion feedback based control system is needed. The aim of this paper is to investigate the use of an ion-current sensor in SI/HCCI engine for direct combustion feedback control. The experimental results obtained, at different speed and loads, show that the estimation of cylinder pressure, through the ion signal, can be performed with high accuracy, and that ion-current has the potential to be a cost effective solution for direct combustion control

Influence of the Variable Valve Timing Strategy on the Control of a Homogeneous Charge Compression (HCCI) Engine

Homogeneous Charge Compression Ignition (HCCI) engine concept has the potential to be high efficient and to produce low NOx and particulate matter emissions. However, the problem of controlling the combustion over the entire load/speed range limits its practical application. The HCCI combustion is controlled by chemical kinetics of the charge mixture, with no influence of the flame diffusion or turbulent propagation. Therefore, to achieve a successful control of the HCCI process, the composition, temperature and pressure of the charge mixture at IVC point have to be controlled. The use of the variable valve timing strategy that enables quick changes in the amount of trapped hot exhaust gases shows the potential for the control of the HCCI combustion. The aim of this paper is to analyse influence of the variable valve timing strategy on the gas exchange process, the process between the first valve open event (EVO) and the last valve closing event (IVC), in a HCCI engine fuelled with standard gasoline fuel (95RON). The gas exchange process affects the engine parameters and charge properties and therefore plays a crucial role in determining the control of the HCCI process. Analysis is performed by the experimental and modelling approaches. The single-cylinder research engine equipped with the fully variable valve train (FVVT) system was used for the experimental study. A combined code consisting of a detailed chemical kinetics code and one-dimensional fluid dynamics code was used for the modelling study. The results obtained indicate that the variable valve timing strategy has a strong influence on the gas exchange process, which in turn influences the engine parameters and the cylinder charge properties, hence the control of the HCCI process. The EVC timing has the strongest effect followed by the IVO timing, while the EVO and IVC timings have the minor effects

Influence of variable valve timings on the gas exchange process in a controlled auto-ignition engine

The controlled auto-ignition (CAI) engine concept has the potential to be highly effcient and to produce low NOx and particulate matter emissions. However, the problem of controlling the combustion over the entire load/speed range limits its practical application. The CAI combustion is controlled by the chemical kinetics of the charge mixture, with no influence of the flame diffusion or turbulent propagation. Therefore, to achieve successful control of the CAI process, the composition, temperature and pressure of the charge mixture at the inlet valve closure (IC ) point have to be controlled. The use of the variable valve timing strategy, which enables quick changes in the amount of trapped hot exchaust gases, shows the potential for control of CAI combustion. The aim of this paper is to analyse the influence of the variable valve timing strategy on the gas exchange process, the process between the first valve open event (EO) and the last valve closing event (IC ), in a CAI engine fuelled with standard gasoline fuel (95RON). The gas exchange process affects the engine parameters and charge properties and therefore plays a crucial role in determining the control of the CAI process. Analysis is performed by experimental and modelling approaches. A single-cylinder research engine equipped with a fully variable valvetrain (FVVT) system was used for the experimental study. A combined code consisting of a detailed chemical kinetics code and one-dimensional fluid dynamics code was used for the modelling study. The results obtained indicate that the variable valve timing strategy has a strong influence on the gas exchange process, which in turn influences the engine parameters and the cylinder charge properties, and hence the control of the CAI process. The EC timing has the strongest effect, followed by the IO timing, while the EO and IC timings have minor effects

The mechanism of an engine hybrid combustion concept with controlled auto ignition and spark ignition

Controlled Auto Ignition (CAI) uses the internal energy of the compressed charge to auto-ignite the mixture. Using internal exhaust gas re-circulation (IEGR) as an indirect control method, CAI offers superior fuel economy and pollutant emission reductions. Practically, this can readily be achieved by a method of early exhaust valve closure and late inlet valve opening to trap a large quantity of exhaust gas residuals within the cylinder from one cycle to the next. Although the emission and fuel economy can be largely improved, the engine power output is limited to part-load conditions only. At high-load, conventional Spark Ignition (SI) is required. In this research, both SI and CAI and the transition between the two were investigated on a single-cylinder research engine equipped with Lotus’ Research Active Valve Train (AVT) System. It was found that the potential hybrid combustion concept is consisted of four regions: conventional spark ignition combustion, spark ignition controlled auto ignition, spark ignition assisted auto ignition, spark ignition free controlled auto ignition