A Four Stroke Camless Engine, Operated in Homogeneous Charge Compression Ignition Mode with Commercial Gasoline

The purpose of the 4-SPACE (4-Stroke Powered gasoline Auto-ignition Controlled combustion Engine) industrial research project is to research and develop an innovative controlled auto-ignition combustion process for lean burn automotive gasoline 4-stroke engines application. The engine concepts to be developed could have the potential to replace the existing stoichiometric / 3-way catalyst automotive spark ignition 4-stroke engines by offering the potential to meet the most stringent EURO 4 emissions limits in the year 2005 without requiring DeNOx catalyst technology. A reduction of fuel consumption and therefore of corresponding CO2 emissions of 15 to 20% in average urban conditions of use, is expected for the « 4-SPACE » lean burn 4-stroke engine with additional reduction of CO emissions. This paper describes the first set of results of different experimental and numerical studies aiming to get such new combustion process in 4-stroke engines within the framework of this European consortium. One of the target of this consortium driven by IFP, is to develop a 4-stroke gasoline engine running conventionally at high load (with a normal compression ratio and without any intake air heating) and able to achieve Controlled Auto-Ignition (CAI) process at part load by reproducing the 2-stroke internal conditions (internal EGR rate and fluid dynamic control, temperature level...) favorable to this particular combustion process. For this purpose and as a starting point of the work program, a production 2-stroke engine known for its part load auto-ignition behavior is fully studied. Such work is focused on the analysis of in-cylinder conditions prior to auto-ignition using combined experimental testing, 3D CFD computations and optical diagnostics. From this analysis, 1D CFD computations have been extensively performed to evaluate the possible 4-stroke concepts able to reproduce internal conditions favorable to CAI. Then, the most “promising” configurations have been experimentally investigated. Encouraging preliminary results have already shown that NOx emissions are reduced by 10 to 40 times and the fuel economy is improved by 8 to 10% when compared with stoichiometric reference conditions. Other ways of getting auto-ignition of the lean fresh mixture are also explored by the project partners. The effects of several parameters, such as the fuel composition, the engine compression ratio, the intake air temperature level, etc... are also included in the research program. Thus, to analyze better analyze intrinsic autoignition process, specific tools as for example Rapid Compression Machine have been developed. Different fuels at various initial conditions (e.g. temperature, excess air) have been tested and compared, for example in terms for example of combustion rate and auto-ignition delay. Results obtained contribute to the better understanding of the auto-ignition process. Preliminary visualization results from specially designed single cylinder engines (2-stroke and 4-stroke) have been obtained for controlled auto-ignition combustion. The effect of charge stratification is briefly discussed.

Innovative Ultra-low NOx Controlled Auto-Ignition Combustion Process for Gasoline Engines: the 4-SPACE Project

We have used the HCT (Hydrodynamics, Chemistry and Transport) chemical kinetics code to simulate HCCI (homogeneous charge compression ignition) combustion of methane-air mixtures. HCT is applied to explore the ignition timing, bum duration, NO x production, gross indicated efficiency and gross IMEP of a supercharged engine (3 atm. Intake pressure) with 14:1, 16:l and 18:1 compression ratios at 1200 rpm. HCT has been modified to incorporate the effect of heat transfer and to calculate the temperature that results from mixing the recycled exhaust with the fresh mixture. This study uses a single control volume reaction zone that varies as a function of crank angle. The ignition process is controlled by adjusting the intake equivalence ratio and the residual gas trapping (RGT). RGT is internal exhaust gas recirculation which recycles both thermal energy and combustion product species. Adjustment of equivalence ratio and RGT is accomplished by varying the timing of the exhaust valve closure in either 2-stroke or 4-stroke engines. Inlet manifold temperature is held constant at 300 K. Results show that, for each compression ratio, there is a range of operational conditions that show promise of achieving the control necessary to vary power output while keeping indicated efficiency above 50% and NO x levels below 100 ppm. HCT results are also compared with a set of recent experimental data for natural gas.

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Compression ratio effect on methane HCCI combustion

The authors have used the HCT (hydrodynamics, chemistry, and transport) chemical kinetics code to simulate HCCI (homogeneous charge compression ignition) combustion of methane-air mixtures. HCT is applied to explore the ignition timing, burn duration, NO{sub X}production, gross indicated efficiency and gross IMEP of a supercharged engine (3 atm. intake pressure) with 14:1, 16:1 and 18:1 compression ratios at 1200 rpm. HCT has been modified to incorporate the effect of heat transfer and to calculate the temperature that results from mixing the recycled exhaust with the fresh mixture. This study uses a single reaction zone that varies as a function of crank angle. The ignition process is controlled by adjusting the intake equivalence ratio and the residual gas trapping (RGT). RGT is internal exhaust gas recirculation, which recycles both thermal energy and combustion product species. Adjustment of equivalence ratio and RGT is accomplished by varying the timing of the exhaust valve closure in either two-stroke or four-stroke engines. Inlet manifold temperature is held constant at 300 K. Results show that, for each compression ratio, there is a range of operational conditions that show promise of achieving the control necessary to vary power output while keeping indicated efficiency above 50 percent andmore » NO{sub X}levels below 100 ppm. HCT results are also compared with a set of recent experimental data for natural gas.« less

/pdf/compression-ratio-effect-on-methane-hcci-combustion-g94fbz04z4.pdf

Compression Ratio Effect on Methane HCCI Combustion

Engine and car manufacturers are experiencing the demand concerning fuel efficiency and low emissions from both consumers and governments. Homogeneous charge compression ignition (HCCI) is an alternative combustion technology that is cleaner and more efficient than the other types of combustion. Although the thermal efficiency and emission of HCCI engine are greater in comparison with traditional engines, HCCI combustion has several main difficulties such as controlling of ignition timing, limited power output, and weak cold-start capability. In this study a literature review on HCCI engine has been performed and HCCI challenges and proposed solutions have been investigated from the point view of Ignition Timing that is the main problem of this engine. HCCI challenges are investigated by many IC engine researchers during the last decade, but practical solutions have not been presented for a fully HCCI engine. Some of the solutions are slow response time and some of them are technically difficult to implement. So it seems that fully HCCI engine needs more investigation to meet its mass-production and the future research and application should be considered as part of an effort to achieve low-temperature combustion in a wide range of operating conditions in an IC engine.

/pdf/homogeneous-charge-compression-ignition-combustion-7jl7hy8vym.pdf

Homogeneous Charge Compression Ignition Combustion: Challenges and Proposed Solutions

A timing controlled auto-ignition name ``AR combustion`` could improve irregular combustion in the part load operation of conventional two-stroke engines. Their previous papers have suggested its idea and the drastic improvements in fuel consumption and HC emission proven through a bench experiments. This time, form a concept that improvements of a two-stroke engine should be done maintaining its original advantages, an AR combustion engine was developed by using a simple exhaust valve and maintaining engine`s original power output. This engine was mounted on a motorcycle and experimented in the ``Dakar rally``. As the results, good fuel economies exceeding a four-stroke rally model, excellent driveability and durability were proven, because of the improvement in the combustion and engine`s potential for the downsizing. The AR combustion engine, consequently, has good prospects for the practical use.

Takaharu Kurosaki

Papers

Analysis on Fuel Economy Improvement and Exhaust Emission Reduction in a Two-Stroke Engine by Using an Exhaust Valve