The research for alternative fuels increased rapidly to mitigate the pollution problems resulting from using conventional fuels in internal combustion engines. Natural gas (NG) appears the most promising alternative due to its low prices and availability around the world.In this paper, a two-zone, zero-dimensional (0-D) model for the simulation of dual fuel NGdiesel engine is developed to study the performance of the engine with a proposed technique of NG early direct injection. The model is composed of several sub-models that are based on semiempirical formulas. NG is modeled as being directly injected at the beginning of the compression stroke. The model is applied to study the performance of HELWAN M-114 diesel engine using dual fuel of NG and diesel fuels as a case study.The results indicate that using NG early direct injection technique (EDI) results in increasing the volumetric efficiency and hence the brake power of the engine compared to the intake manifold induction (IMI) of NG with air through the intake manifold. The percentage increase in brake power is 8.7% at NG mass ratio in the total fuel (the supplement ratio (SR)) of 90% at full load. To evaluate the proposed technique, results obtained by varying the engine load and the SR. Results indicate that the slow burning rate of NG results in decrease in the brake thermal efficiency by 3.5% and increases in brake specific fuel consumption with a percentage of 10.2% at 90% SR and full load. However, a great advantage of increasing the SR is the reduction in NO x and soot emissions particularly at high engine loads where they were reduced with percentages of 28.6% and 86%, respectively at 90% SR and full load condition.

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Solar greenhouses can be considered as efficient places for biological CO 2 capture and utilization if CO 2 enrichment becomes a common practice there. As CO 2 enrichment is applied only when greenhouses are closed, ventilated greenhouses--which represent a large percentage of greenhouses all over the world--cannot be considered for this practice. Consequently, ventilated greenhouses cannot be considered for CO 2 capture and utilization. The aim of this paper is to show--through modeling and simulation--that these ventilated greenhouses can be activated for serving as efficient CO 2 capture and utilization places if they are kept closed (to apply CO 2 enrichment) and used microclimate control methods alternative to ventilation. The paper introduces a realistic mathematical model in which all the processes and phenomena associated with the biological CO 2 capture and utilization by photosynthesis inside greenhouses are considered. The model validity and accuracy were ensured through the good agreement of its numerical predictions with the available experimental results in the literature. The effect of different environmental and planting conditions on the CO 2 capturing process (the photosynthesis process) is investigated. A case study was chosen to investigate the effects of the cooling method, cooling temperature, planting conditions, and CO 2 concentration level on the cumulative amount of captured CO 2 which represents the greenhouse capturing performance.The results show that the capturing performance of greenhouse can be enhanced from value as low as 1.0 g CO 2 / m 2 day for ventilated greenhouses with low planting density to a value as high as 140 g CO 2 /m 2 day for high planting density when alternative microclimate control methods and CO 2 enrichment are applied, considering the appropriate plant type. Additional benefits besides CO 2 capture are also discussed for the possible increase of the plant productivity and possible lowering of water consumption by plants. Keywords

This paper investigates the thermodynamic performance of all 3--process, work-producing cycles for non-reacting perfect gases. Out of. the 18 possible combinations of cycles composed of 3 processes, there are only 8 cycles which can produce work. The analysis studies the effect of cycle parameters on cycle performance. The performance is reflected by the first and second law efficiencies n/ and :III and dimensionless heat and available energy input gin(=Qin/cv Tmin) and ain(=Ain/cv Tmin) respectively. The parameters in dimensionless form are: compression ratio r(=maximum to minimum volume ratio), specific heat ratio k, minimum to ambient temperature ratio Tmin/To, maximum to minimum temperature and pressure ratios Tmax/Tmin and Pmax/Pmin respectively.The study shows that in the suggested practical range of application (r < 30, Tmax/Tmin 10, Pmax/P min < 100 and T min/T0=1.0) n i and n11 vary between 20 to 72% and 25 to 100% respectively. The analysis methodology presented here could be a main tool in the performance investigation and design of more complicated cycles.