Compression-Ignited Homogeneous Charge Combustion

Homogeneous charge compression ignition (HCCI) is a new combustion technology that may develop as an alternative to diesel engines with high efficiency and low NO x and particulate matter emissions. This paper describes the HCCI research activities being currently pursued at Lawrence Livermore National Laboratory and at the University of California Berkeley. Current activities include analysis as well as experimental work.On analysis, we have developed two powerful tools: a single zone model and a multi-zone model. The single zone model has proven very successful in predicting start of combustion and providing reasonable estimates for peak cylinder pressure, indicated efficiency and NO X emissions. This model is being applied to develop detailed engine performance maps and control strategies, and to analyze the problem of engine startability. The multi-zone model is capable of very accurate predictions of the combustion process, including HC and CO emissions. The multi-zone model has applicability to the optimization of combustion chamber geometry and operating conditions to achieve controlled combustion at high efficiency and low emissions.On experimental work, we have done a thorough evaluation of operating conditions in a 4-cylinder Volkswagen TDI engine. The engine has been operated over a wide range of conditions by adjusting the intake temperature and the fuel flow rate. Satisfactory operation has been obtained over a wide range of operating conditions. Cylinder-to-cylinder variations play an important role in limiting maximum power, and should be controlled to achieve satisfactory performance.

Section: Analysis Of Hcci Combustionmentioning

confidence: 99%

HCCI Combustion: Analysis and Experiments

Aceves¹,

Flowers²,

Martínez-Frías³

et al. 2001

“…In 1983 Njat and Foster showed that it was also possible to achieve HCCI in a four stroke engine [8]. They used an engine with variable compression operating on a mixture of iso-octane and n-heptane.…”

Section: Introductionmentioning

confidence: 99%

Supercharged Homogeneous Charge Compression Ignition

Christensen¹,

Johansson²,

Amnéus

et al. 1998

290

150

The Homogeneous Charge Compression Ignition (HCCI) is the third alternative for combustion in the reciprocating engine. Here, a homogeneous charge is used as in a spark ignited engine, but the charge is compressed to auto-ignition as in a diesel. The main difference compared with the Spark Ignition (SI) engine is the lack of flame propagation and hence the independence from turbulence. Compared with the diesel engine, HCCI has a homogeneous charge and hence no problems associated with soot and NO X formation. Earlier research on HCCI showed high efficiency and very low amounts of NO X , but HC and CO were higher than in SI mode. It was not possible to achieve high IMEP values with HCCI, the limit being 5 bar. Supercharging is one way to dramatically increase IMEP. The influence of supercharging on HCCI was therefore experimentally investigated. Three different fuels were used during the experiments: isooctane, ethanol and natural gas. Two different compression ratios were used, 17:1 and 19:1. The inlet pressure conditions were set to give 0, 1 or 2 bar of boost pressure. The highest attainable IMEP was 14 bar using natural gas as fuel at the lower compression ratio. The limit in achieving even higher IMEP was set by the high rate of combustion and a high peak pressure.Numerical calculations of the HCCI process have been performed for natural gas as fuel. The calculated ignition timings agreed well with the experimental findings. The numerical solution, is however, very sensitive to the composition of the natural gas.

“…Other factors such as heat rejection to chamber walls, and degree of cycle-to-cycle variation in the gas exchange process were also found to be important. Najt and Foster [7] was the first to apply the CAI combustion technology to a 4-stroke gasoline engine through intake charge heating. By means of heat release analysis and cycle simulation, they showed that the CAI ignition process was governed by low temperature (< 950 K) hydrocarbon oxidation kinetics.…”

Section: Introductionmentioning

confidence: 99%

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

Zhao

Jian

et al. 2002

166

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.