Abstract
In this paper, the air-fuel ratio regulation problem of compressed natural gas (CNG) engines considering stochastic L2 disturbance attenuation is researched. A state observer is designed to overcome the unmeasurability of the total air mass and total fuel mass in the cylinder, since the residual air and residual fuel that are included in the residual gas are unmeasured and the residual gas reflects stochasticity. With the proposed state observer, a stochastic robust air-fuel ratio regulator is proposed by using a CNG engine dynamic model to attenuate the uncertain cyclic fluctuation of the fresh air, and the augmented closed-loop system is mean-square stable. A validation of the proposed stochastic robust air-fuel ratio regulator is carried out by the numerical simulation of two working conditions. The accuracy control of the air-fuel ratio is realized by the proposed stochastic robust air-fuel ratio regulator, which in turn leads to an improvement in fuel economy and emission performance of the CNG engines.
Highlights
Natural gas is an acknowledged appropriate optional fuel, since it is characterized by clean combustion, a preferable fuel economy, richness, and low cost among various alternative fuels
To calculate the airfuel ratio in the chamber of precombustion, a model reflecting various fuel flow rates and mixtures was established in [2]. e emission and combustion performance affected by compression ratio of natural gas engines with excess hydrogen in the case of various air-fuel ratios was investigated in [3] through experiments. e results on the performance of the emission and combustion of natural gas engines, which were affected by the composition of natural gas, were reviewed in [4]. e emissions of particles were researched in [5] for a natural gas engine, and experiments were conducted with a natural gas engine that was modified from a gasoline-fuelled engine. e cyclic variation in the combustion in natural gas engines with premixed and lean burn characteristics was discussed in [6]
Integrated effects of injection timing and boost pressure on combustion and performance of a direct injection compressed natural gas (CNG) engine were researched in [8], and the experimental results demonstrated that an improvement was achieved when the boost pressures were larger than 7.5 Kpa at every operating point
Summary
Natural gas is an acknowledged appropriate optional fuel, since it is characterized by clean combustion, a preferable fuel economy, richness, and low cost among various alternative fuels. E emission and combustion performance affected by compression ratio of natural gas engines with excess hydrogen in the case of various air-fuel ratios was investigated in [3] through experiments. It is known that, the fuel economy and emissions of CNG engines are heavily affected by the control accuracy of the in-cylinder air-fuel ratio, which is defined as the ratio of the total air mass to the total fuel mass in the cylinder. A state observer-based stochastic robust air-fuel ratio regulator is presented to overcome the errors in the estimation of the masses of the total air and the total fuel, and the fluctuation of the fresh air mass, which prominently influence the accuracy of the air-fuel ratio control of CNG engines. By using the designed stochastic robust air-fuel ratio regulator, the fuel economy and emission performance of the CNG engines will be enhanced. From which we can obtain that the air-fuel ratio is a linear function of y(k)
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