The global policy solution seeks to reduce the usage of fossil fuels and greenhouse gas (GHG) emissions, and biogas (BG) represents a solutions to these problems. The use of biogas could help cope with increased amounts of waste and reduce usage of fossil fuels. Biogas could be used in compressed natural gas (CNG) engines, but the engine electronic control unit (ECU) needs to be modified. In this research, a spark ignition (SI) engine was tested for mixtures of biogas and hydrogen (volumetric hydrogen concentration of 0, 14, 24, 33, and 43%). In all experiments, two cases of spark timing (ST) were used: the first for an optimal mixture and the second for CNG. The results show that hydrogen increases combustion quality and reduces incomplete combustion products. Because of BG’s lower burning speed, the advanced ST increased brake thermal efficiency (BTE) by 4.3% when the engine was running on biogas. Adding 14 vol% of hydrogen (H2) increases the burning speed of the mixture and enhances BTE by 2.6% at spark timing optimal for CNG (CNG ST) and 0.6% at the optimal mixture ST (mixture ST). Analyses of the rate of heat release (ROHR), temperature, and pressure increase in the cylinder were carried out using utility BURN in AVL BOOST software.

Biogas is one of the alternative solutions that could reduce the usage of fossil fuels and production of greenhouse gas emissions, as biogas is considered as an alternative fuel with a short carbon cycle. During biogas production, organic matter is decomposed during an anaerobic digestion process. Biogas mainly consists of methane and carbon dioxide, of which the ratio varies depending on the raw material and parameters of the production process. Therefore, engine parameters should be adjusted in relationship with biogas composition. In this research, a spark ignition engine was tested for mixtures of biogas with 0 vol%, 20 vol%, 40 vol% and 50 vol% of CO2. In all experiments, two cases of spark timing (ST) were used; the first one is a constant spark timing (26 crank angle degrees (CAD) before top dead center (BTDC)) and the second one is an advanced spark timing (optimal for biogas mixture). Results show that increasing the CO2 concentration and using constant spark timing increases the mass burned fraction combustion duration by 90%, reduces the in-cylinder pressure and leads to a reduction in the brake thermal efficiency and nitrogen oxides emissions at all measurement points. However, the choice of optimal spark timing increases the brake thermal efficiency as well as hydrocarbon and CO2 emission.

This article presents a change in the indicators of a compression ignition (CI) engine by replacing conventional diesel fuel (D100) with pure chicken fat (F100) and mixtures of these fuels. Mixtures of diesel and fat with volume ratios of 70/30, 50/50 and 30/70 were used. Research of the fuel properties was conducted. In order to reduce the fuel viscosity, blends of fat and diesel were heated. The experimental research was conducted at different engine loads with exhaust gas recirculation (EGR) both off and on. The conducted analysis of the combustion process revealed a significant change in the rate of heat release (ROHR) when replacing diesel with chicken fat. Chicken fat was found to increase the CO2 and CO emissions, leaving hydrocarbon (HC) emissions nearly unchanged. Having replaced the D100 with diesel and chicken fat mixtures or F100, a significant reduction in smoke and nitrogen oxide (NOx) emissions was observed when EGR was off. When EGR was on, the smoke level increased, but the blends with chicken fat reduced it significantly, and the increased fat content in the fuel mixture reduced the NOx emissions. The engine’s brake specific fuel consumption (BSFC) increased while the brake thermal efficiency (BTE) decreased, having replaced conventional diesel with chicken fat due to differences in the fuel energy properties and the combustion process.

Biogas has increasingly been used as an alternative to fossil fuels in the world due to a number of factors, including the availability of raw materials, extensive resources, relatively cheap production and sufficient energy efficiency in internal combustion engines. Tightening environmental and renewable energy requirements create excellent prospects for biogas (BG) as a fuel. A study was conducted on a 1.6-L spark ignition (SI) engine (HR16DE), testing simulated biogas with different methane and carbon dioxide contents (100CH4, 80CH4_20CO2, 60CH4_40CO2, and 50CH4_50CO2) as fuel. The rate of heat release (ROHR) was calculated for each fuel. Vibration acceleration time, sound pressure and spectrum characteristics were also analyzed. The results of the study revealed which vibration of the engine correlates with combustion intensity, which is directly related to the main measure of engine energy efficiency—break thermal efficiency (BTE). Increasing vibrations have a negative correlation with carbon monoxide (CO) and hydrocarbon (HC) emissions, but a positive correlation with nitrogen oxide (NOx) emissions. Sound pressure also relates to the combustion process, but, in contrast to vibration, had a negative correlation with BTE and NOx, and a positive correlation with emissions of incomplete combustion products (CO, HC).

Numerical simulations of Nissan Qashqai HR16DE engine with increased compression ratio from 10,7:1 to 13,5:1 was carried out using AVL BOOST software. Modelled engine work cycles while engine works with biogas (BG) and hydrogen (H2) mixtures. For biogas used mixture of 35 % carbon dioxide (CO2) and 65 % methane (CH4). Three mixtures of biogas with added 5 %, 10 % and 15 % H2 was made. The simulation of engine work cycles was performed at fully opened throttle and changing engine crankshaft rotation speeds: ne1 = 1500, ne2 = 3000, ne3 = 4500, ne4 = 6000 rpm. Simulation results demonstrated what adding hydrogen to biogas increase in-cylinder temperature and nitrogen oxides (NOx) concentration because of higher mixtures lower heating values (LHV) and better combustion process. Other emissions of carbon monoxide (CO) and hydrocarbons (HC) decreased while adding hydrogen due to the fact that hydrogen is carbon-free fuel.