Performance and Analysis of a 4-Stroke Multi-Cylinder Gasoline Engine with CAI Combustion

Abstract

Controlled Auto-Ignition (CAI) combustion was realised in a production type 4-stroke 4-cylinder gasoline engine without intake charge heating or increasing compression ratio. The CAI engine operation was achieved using substantially standard components modified only in camshafts to restrict the gas exchange processThe engine could be operated with CAI combustion within a range of load (0.5 to 4 bar BMEP) and speed (1000 to 3500 rpm). Significant reductions in both specific fuel consumption and CO emissions were found. The reduction in NOx emission was more than 93% across the whole CAI range. Though unburned hydrocarbons were higher under the CAI engine operation.In order to evaluate the potential of the CAI combustion technology, the European NEDC driving cycle vehicle simulation was carried out for two identical vehicles powered by a SI engine and a CAI/SI hybrid engine, respectively. The simulation results showed only moderate improvement in fuel economy and exhaust emissions because of low utilisation of CAI during the drive cycle.In order to take full advantage of the CAI combustion technology, detailed analyses were carried out on the engine's performance, heat release and combustion characteristics, emissions and the effect of gas exchange processes. These analyses showed that the engine's performance and emissions were mainly affected by the trapped residual fractions and residual temperature. In addition, the backflow was found to affect the combustion and emission as well.

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

“…the temperature of the exhaust gas (measured in the exhaust manifold) decreases with the earlier EVC-the increase in the amount of TRG (Refer to Figure 5). Similar observations have been reported from other experiments [25,26].…”

“…The mixture in this region will be expected to auto-ignite later than the mixture in first region and to produce a higher heat release rate and peak cylinder pressure. This observation has been reported in [21,25].…”

“…It can be expected that this mixture will auto-ignite relatively early in the following cycle, producing a less intense heat release rate (longer combustion duration) and low peak cylinder pressure. This behaviour has been reported in [21,25].…”

“…The charge mixture in this region has a high temperature combined with a high dilution which is very favourable for the HCCI combustion as discussed in [17,21,25]. It can be expected that this mixture will auto-ignite relatively early in the following cycle, producing a less intense heat release rate (longer combustion duration) and low peak cylinder pressure.…”

CAI Combustion of Gasoline and its Mixture with Ethanol in a 2-Stroke Poppet Valve DI Gasoline Engine

“…Many approaches have been attempted to achieve CAI operation on the 4-stroke spark ignition engines, such as intake air heating, high compress ion ratio, dual fuel, recycling the exhaust gas, and so on [2]. Amongst these approaches , internally recycling the exhaust gas, such as residual gas trapping [3][4][5][6] and exhaust gas rebreathing [7], have been proved most effective in achieving CAI combustion and demonstrated their potential to be incorporated in the production gasoline engine.…”