Fueled Homogeneous Charge Compression Ignition Research Articles

Simulation Analysis of Combustion Parameters and Emission Characteristics of CNG Fueled HCCI Engine

The naturally aspirated compressed natural gas (CNG) fueled homogeneous charge compression ignition (HCCI) engine operation region is narrow between heavy knock at rich air-fuel mixture side and misfire at the lean air-fuel mixture side. However, high activation energy is needed to attain autoignition temperature of CNG fueled HCCI engine. This paper seeks to provide guidance in overcoming challenges of CNG fueled HCCI engine by using CHEMKIN. It is used to investigate the fundamental characteristics of the homogeneous charge compression ignition combustion process for different air-fuel mixture inlet temperature, relative air-fuel ratio of 2.5, and with hemispherical bowl types of combustion chambers. The variation of various properties like the peak cylinder pressure, peak cylinder temperature, CO emission, NO emission, soot emission, and HC emission are studied. It is necessary to develop new combustion models to simulate and predict all parameters with high accuracy.

Experimental and Skeletal Kinetic Model Study of Compressed Natural Gas Fueled Homogeneous Charge Compression Ignition Engine

Problem statement: In homogeneous charge compression ignition engines fuel oxidation chemistry determines the auto-ignition timing, heat release, reaction intermediates and the ultimate products of combustion. To shorten development time and to understand combustion processes, the use of simulation is increasing. Approach: A model that correctly simulates fuel oxidation at these conditions would be a useful design tool. Detailed models of hydrocarbon fuel oxidation, consisting of hundreds of chemical species and thousands of reactions. A way to lessen the burden was to use a skeletal reaction model, containing only tens of species and reactions. Results: The model was developed from the existing pre-ignition model, which had 10 species, 5 elementary reactions for kinetic and 6 elementary reactions for equilibrium and the standard k-? turbulence model had been used in this investigation. This model combines the chemistry of the low, intermediate and high temperature regions. Conclusion: Simulations are compared with measured and calculated data from the engine operating at the following conditions: speed 1500 RPM, inlet temperature 363-433 K, fuel CNG and ? range 3-5. The simulations are generally in good agreement with the experimental data including temperature, pressure, combustion duration and ignition delay and heat release.

Exploring Strategies for Reducing High Intake Temperature Requirements and Allowing Optimal Operational Conditions in a Biogas Fueled HCCI Engine for Power Generation

This paper evaluates strategies for reducing the intake temperature requirement for igniting biogas in homogeneous charge compression ignition (HCCI) engines. The HCCI combustion is a promising technology for stationary power generation using renewable fuels in combustion engines. Combustion of biogas in HCCI engines allows high thermal efficiency similar to diesel engines, with low net CO2 and low NOx emissions. However, in order to ensure the occurrence of autoignition in purely biogas fueled HCCI engines, a high inlet temperature is needed. This paper presents experimental and numerical results. First, the experimental analysis on a 4 cylinder, 1.9 L Volkswagen TDI diesel engine running with biogas in the HCCI mode shows high gross indicated mean effective pressure (close to 8 bar), high gross indicated efficiency (close to 45%) and NOx emissions below the 2010 US limit (0.27 g/kWh). Stable HCCI operation is experimentally demonstrated with a biogas composition of 60% CH4 and 40% CO2 on a volumetric basis, inlet pressures of 2–2.2 bar (absolute), and inlet temperatures of 200–210 °C for equivalence ratios between 0.19–0.29. At lower equivalence ratios, slight changes in the inlet pressure and temperature caused large changes in cycle-to-cycle variations, while at higher equivalence ratios these same small pressure and temperature variations caused large changes to the ringing intensity. Second, numerical simulations have been carried out to evaluate the effectiveness of high boost pressures and high compression ratios for reducing the inlet temperature requirements while attaining safe operation and high power output. The one zone model in Chemkin was used to evaluate the ignition timing and peak cylinder pressures with variations in temperatures at intake valve close (IVC) from 373 to 473 K. In-cylinder temperature profiles between IVC and ignition were computed using Fluent 6.3 and fed into the multizone model in Chemkin to study combustion parameters. According to the numerical results, the use of both higher boost pressures and higher compression ratios permit lower inlet temperatures within the safe limits experimentally observed and allow higher power output. However, the range of inlet temperatures allowing safe and efficient operation using these strategies is very narrow, and precise inlet temperature control is needed to ensure the best results.

Use of a single-zone thermodynamic model with detailed chemistry to study a natural gas fueled homogeneous charge compression ignition engine

A single zone thermodynamic model with detailed chemical kinetics was used to simulate a natural gas fueled homogeneous charge compression ignition (HCCI) engine. The model employed Chemkin and used chemical kinetics for natural gas with 53 species and 325 reactions. This simulation was used to complete analyses for a modified 0.4 L single cylinder engine. The engine possessed a compression ratio of 21.5:1, and had a bore and stroke of 86 and 75 mm, respectively. Several sets of parametric studies were completed to investigate the minimal initial temperature, engine performance, and nitric oxide emissions of HCCI engine operation. The results show significant changes in combustion characteristics with varying engine operating conditions. Effects of varying equivalence ratios (0.3–1.0), engine speeds (1000–4000 RPM), EGR (0–40%), and fuel compositions were determined and analyzed in detail. In particular, every 0.1 increase in equivalence ratio or 500 rpm increase in engine speed requires about a 5 K higher initial temperature for complete combustion, and leads to around 0.7 bar increase in IMEP.

A Detailed Chemistry Multi-cycle Simulation of a Gasoline Fueled HCCI Engine Operated with NVO

A previously developed Stochastic Reactor Model (SRM) is used to simulate combustion in a four cylinder in-line four-stroke naturally aspirated direct injection Spark Ignition (SI) engine modified to run in Homogeneous Charge Compression Ignition (HCCI) mode with a Negative Valve Overlap (NVO). A portion of the fuel is injected during NVO to increase the cylinder temperature and enable HCCI combustion at a compression ratio of 12:1. The model is coupled with GT-Power, a one-dimensional engine simulation tool used for the open valve portion of the engine cycle. The SRM is used to model in-cylinder mixing, heat transfer and chemistry during the NVO and main combustion. Direct injection is simulated during NVO in order to predict heat release and internal Exhaust Gas Recycle (EGR) composition and mass. The NOx emissions and simulated pressure profiles match experimental data well, including the cyclic fluctuations. The model predicts combustion characteristics at different fuel split ratios and injection timings. The effect of fuel reforming on ignition timing is investigated along with the causes of cycle to cycle variations and unstable operation. A detailed flux analysis during NVO unearths interesting results regarding the effect of NOx on ignition timing compared with its effect during the main combustion. © 2009 SAE International.

A Study on Natural Gas Fueled Homogeneous Charge Compression Ignition Engine (Second Report)

A Study on Natural Gas Fueled Homogeneous Charge Compression Ignition Engine (Second Report)

Ignition control of methane fueled homogeneous charge compression ignition engines using additives

Homogeneous charge compression ignition 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. In this paper, the effect of additives such as dimethyl ether (DME), formaldehyde (CH 2O) and hydrogen peroxide (H 2O 2) for the control of ignition in natural-gas HCCI engines have been investigated numerically by adopting a single-zone zero-dimensional model. The chemical kinetic mechanism incorporated the GRI-3.0 mechanism that considers 53 species and 325 reactions together with the DME reaction scheme consisting of 79 species and 351 reactions. To simulate HCCI engine cycles, a variable volume computation has been performed by including a piston motion into the SENKIN code at a fixed equivalence ratio of 0.3 and initial mixture pressure of 1.5 bar. It was found that an additive-free mixture did not ignite for the intake temperature of 400 K. A mixture containing a small quantity of additives at the same temperature was ignited. For a fixed quantity of additive, it was found that H 2O 2 addition was effective in advancing the ignition timing as compared to the other two additives. It was found that the percentage of additives required to achieve a near TDC ignition timing increases linearly with the increase in the engine speed while decreases with the increase in the equivalence ratio with the superiority of H 2O 2. Furthermore, the addition of even 7% by volume of H 2O 2 could ignite a mixture at an intake temperature of 350 K, while at least the fractions of 12.5% and 35% by volume were needed for DME and CH 2O, respectively. It was also found that the mass fraction of NO with CH 2O addition was less than that with H 2O 2 addition. At the same time, however, a near TDC ignition timing resulted in a similar amount of NO for both additives. Overall, the enhanced reactivity of CH 4 in the presence of small amounts of additives could be used in HCCI engines fueled with methane to alleviate the high intake temperature requirements.

Improvement of Performance in a Natural-Gas Fueled Homogeneous Charge Compression Ignition Engine with Supercharged

A supercharged natural gas compression ignition engine has been tested to confirm the performance as ell as the exhaust gas characteristics. The supercharging improved the thermal effciency through the improvement of the combustion efficiency, the mechanical efficiecy, and the cooling loss. The indicated thermal efficiency becomes the highest when in-cylinder temperature is about 1700 K, due to the improved combustion efficiency and the decrease of cooling loss. The supercharging also reduces the NOx emission. This is because the maximum temperature is kept low while the combustion efficiency is kept high compared with the natural aspiration. The pressure at auto-ignition inceased in case the boost pressure is raised. However, the auto-ignition temperature is the same and 1000-1030K.

Effect of Internal Exhaust Gas Recirculation on Performance and Emissions from a Natural-Gas Fueled Homogeneous Charge Compression Ignition Engine

Besides the narrow operation range, natural gas fueled HCCI engine requires higher compression ratio and pre-heated air due to the low Cetan number. In this study, influences of the internal EGR ratio on the performance and the emissions of a single cylinder engine were investigated. Although the internal EGR lowers the permissible temperature of the intake air, it also decrease the indicated thermal efficiency. This is attributed to the increase of heat loss and pumping loss. The effect of internal EGR varies depending on the air temperature. At high air temperature, it increase the combustion duration. By contrast, at low temperature it increases the inner gas temperature at the start of compression phase, and thus, decreases the combustion duration. Under the turbo charged condition, the indicated thermal efficiency and the indicated mean effective pressure are increased. Those are attributed to the decreases of the heat loss.

Performance and Exhaust Emission in a Natural-Gas Fueled Homogeneous Charge Compression Ignition Engine

An experimental study was performed to clarify the operation condition on natural gas fueled homogeneous charge compression ignition engine. Using a single cylinder engine, operation range, engine performance and exhaust emissions were measured under various intake air temperature, compression ratio and equivalence ratio. Under the high intake air temperature, combustion efficiency is high, but under lower temperature, engine was operated in narrow A/F range. The use of high compression ratio, engine was operated at lower intake air temperature. To keep combustion efficiency over 80% and NOx emission under 10 ppm, maximum in-cylinder temperature should be controlled within the narrow range between 1 500 K and 1 800 K. Natural gas auto-ignited over 1 000 K and the effect of A/F was low. Auto ignition temperature was decreased according to the decline of intake air temperature.