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

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

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

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

Intelligent coolant control – a potential technology to improve controlled auto ignition combustion

Controlled Auto Ignition (CAI) uses compression heat to auto ignite a homogeneous air/fuel mixture in an internal combustion engine. 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 a large quantity of exhaust gas residuals within the cylinder from one cycle to the next. However, it has been found that the IEGR promoted CAI combustion largely depends on the quantity and quality of the IEGR, which in turn depends upon the combustion quality of previous cycle, engine speed, load, etc. At low loads, where the overall engine temperature is low, although an extra large amount of IEGR has been used, CAI becomes difficult to achieve. At high loads, the IEGR is much hotter. The CAI combustion is so strong that it may potentially be converted into detonation combustion. It is difficult to control the CAI combustion quality without external interferences. Engine coolant controls engine heat transfer performance. By physically adjusting its temperature, it was found in this research that IEGR promoted CAI combustion can be significantly extended by increasing engine coolant temperature

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%

The impact on engine performance of controlled auto ignition versus spark ignition with two methods of load control

This paper presents and discusses results taken from Lotus’ Research Active Valve Train (AVT) engine, in which advanced combustion strategies can easily be investigated because of a the functionality of its Fully Variable Valve Train. In particular, Controlled Auto Ignition can readily be initiated and controlled 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. The paper looks at the impact on fuel consumption and emissions (engine out BSNOx, BSTHC and BSCO) of Controlled Auto Ignition versus Spark Ignition with load control either by conventional variable density throttling or by Early Inlet Valve Closure with variable lift. The points analysed are commonly used emissions comparison points: 1300rpm 2.95bar BMEP, 1500rpm 2.62bar BMEP, 2000rpm 2bar BMEP and 2500rpm 2.62bar BMEP