Experimental Evaluation of a Lignocellulosic Biomass Downdraft Gasifier on a Small-Scale Basis: A Thermodynamic Approach

Abstract

This research study explores the technology of biomass syngas production by using an experimental downdraft fixed-bed gasifier coupled to a two-cylinder engine, designed and implemented at the Polytechnic University of Valencia, Spain. Furthermore, it deals with the study of the experimental and analytical relations between the driving thermodynamic parameters that control the gasification process, in order to contribute to the development of a theoretical model for the design of a small-scale gasification facility. Different experiments have been performed to investigate the variations in parameters such as low heating values, the air–syngas ratio, the reduction and combustion temperature, efficiency, and electrical power generation during the continuous functioning of the gasification power production facility. The results obtained show that the low heating value is directly related to the inlet air flow rate, so that it increases when the air flow increases, while the increase in the inlet air flow of the gasifier makes both the reduction and the combustion temperature increase. Moreover, the efficiency of the motor–generator reaches a maximum value of 0.204 at the maximum power (around 5 kW), being characterized by an excellent operating range for the air–fuel ratio of a gasification facility.

1. Introduction

According to the sustainable development scenario, the use of biofuel produced by biomass for power production is expected to increase and provide 2% of the total world supply by 2030, equating to 4% within the Organization for Economic Cooperation and Development area (OECD) [1]. Due to the emerging policies for the reduction in greenhouse gas emissions, lignocellulosic biomass gasification coupled with solar photovoltaics [2] is classified as one of the renewable energy sources with the potential to replace conventional fossil fuels [3,4].

Gasification is a complex technology that converts biomass into a synthesis gas called syngas. The use of syngas for power generation is a growing industry with high potential for reducing greenhouse gas emissions [5]. Biomass gasification for power generation has been implemented in developed countries across Europe, North America, and Asia in the form of multiple small-scale biomass gasification systems [6]. However, the potential for uptake of biomass gasification is more promising in developing countries where access to the electrical grid is possibly limited and the cost for the necessary extensions of the existing electrical network might be economically unviable [7]. Gasified biomass is a green and sustainable resource that can play a significant role in the context of a Circular Economy (CE). The CE has emerged as an opportunity to achieve meaningful decarbonization across the value chain where the three R’s related to this concept (reduce, re-use, and recycle) aim to make the best possible use of society’s resources. This can be accomplished through the utilization of biomass from raw materials to produce syngas, which can support the achievement of CE goals and prove beneficial to a range of biomass producers including forest owners. Hence, biomass gasification has the potential to turn waste into valuable green fuels [8].

Despite the benefits of gasified biomass, there are some challenges that still must be overcome. Mainly, the unpredictable availability of biomass resources and a lack of uniformity in its composition, in addition to the existence of a wide range of apparatus designs and set-ups, many of which are still at the research stage, are among the notable challenges [9,10].

Moreover, previous studies showed biomass gasification as a technology not yet mature enough for large-scale applications and is still in need of costly and time-consuming research to achieve stable behavior and high performance [11]. Due to these factors, governmental subsidies and incentives are still crucial for the upscaling of syngas gasifiers’ development [12]. In particular, the fixed-bed downdraft gasifier configuration is a well-established technology, characterized by the production of syngas with low tar content [13] but is difficult to scale up and better suited to small-scale power generation applications [14]. The influence of operational parameters are still the principal factors that need to be analyzed in order to achieve a stable and efficient process [15].

This research study explores the technology of biomass syngas production by using an experimental fixed-bed downdraft gasifier coupled to a two-cylinder engine. Further-more, it studies the experimental and analytical relationships between the driving thermodynamic parameters that control the gasification process, in order to contribute to the development of a theoretical model for the design of a small-scale gasification facility while helping to overcome the remaining technological barriers to its development. In-deed, the gasifier used in this research was built at the IIE-UPV lab as reactors of this kind are difficult to be found commercially. In order to make progress in this field, different experiments have been performed to investigate variations in parameters such as low heating values, the air–syngas ratio, the reduction and combustion temperature, efficiency, and electrical power generation during the functioning of the power production facility with the aim of opening the gate to future research focused on the study of the use of a four-cylinder engine for higher-scale power generation.

This work is organized as follows: Research background on biomass gasification and the most recent advancements on this topic are presented in Section 2. Section 3 is devoted to describing the main characteristics of the biomass used in the gasifier, the architecture of the whole downdraft gasification facility designed and implemented in the laboratory, and the methodology followed to perform the experiments. The parameters driving the gasification process are explained in Section 4, while the main results obtained during the experiments are discussed in Section 5. Finally, the conclusions of this analysis are stated in Section 6.

2. Research Background

Biomass gasification is an alternative thermo-chemical conversion process to combustion that enables the production of syngas through an oxidation process at temperature around 1000 °C [16]. The viability of this fuel conversion process resides on the favorable characteristics of the produced fuel (syngas) such as high calorific value, low tar content, and high conversion yield. Previous studies proved that such parameters as yield, syngas composition, or tar quantity are dependent on the type of biomass used, the pressure drop, and the temperatures reached in the process, but discrepancies in the recommended operation values of the key gasification parameters still exist and require additional and more precise studies [17].

2.1. Fixed-Bed Downdraft Gasifiers

Some advancements have been made in fixed-bed gasifiers, which have enabled synthesis gas production of different qualities depending on the chosen operating temperature for the facility. In particular, the fixed-bed downdraft gasifier configuration is a well-established and consolidated technology characterized by a production of syngas with low tar content [13,18,19] but is difficult to scale up and is better suited to small-scale power generation applications [14,20]. Indeed, the lower construction costs and easy operation make fixed-bed downdraft gasifiers appealing for small-scale applications [21]. Controversially, they are more sensitive to biomass properties than fluidized-bed reactors, so more research efforts are necessary in order to establish the relation between the quality and yield of the produced syngas from different types of biomass, or how the use of different biomasses affects the performance of the same gasifier [16].

2.2. Biomass Resources

Among the different kinds of biomass, lignocellulosic biomass is the most abundant in the world, with an estimated production of 181.5 billion tons annually [22]. However, the availability of biomass in terms of quantity, quality, and price is affected due to the absence of regulation for a specific market for biomass resources.

Multiple types of lignocellulosic biomass are currently suitable for gasification. There are little experimental results available in the literature so far. One of them is presented by Prasad et al., who tested pongamia residue (shells), which is one of the most abundant biomasses in developing countries, obtaining pellets with a bulk density of 146 kg/m³ [23]. On the other side, Alnouss et al. carried out a study in Qatar demonstrating the benefits of a biomass blend composed of date palm residues, sewage sludge, and livestock manure, which helped to overcome the handicap of seasonal biomass availability [24].

There are recent examples of research conducted with different kinds of biomass to produce syngas. Thus, Alves-Magalhaes et al. [16], investigated the behavior of a fixed-bed gasifier fed with different types of biomass resources, including eucalyptus woodchips, pine pellets, and eucalyptus charcoal. On the other side, Zachl et al. [25] successfully tested a commercial small-scale open-top gasifier to produce syngas from forest woodchips. Other kinds of traditional biomass such as sawdust have also been used, mixed with personal care waste like sanitary napkins, as presented by Deore et al. [26] for the production of syngas in a downdraft gasifier for thermal applications.

New biomass sources have also been explored. Among them, water hyacinth has resulted in one of the most appropriate sources of primary fuel due to its wide availability, being an invasive species all over the globe, and has demonstrated favorable characteristics for cheap biofuel production. In fact, water hyacinth contains a large quantity of cellulose that can be converted into bioethanol by enzymes to power vehicles and motors, as well as biogas to generate electricity by using thermal gasification (>500 °C) [27,28].

Recently, new research lines focused on maximizing hydrogen content in the biomass gasification process have been developed. The objective is to produce syngas enriched with hydrogen as a result of thermochemical gasification [15,29,30].

In spite of that, there is a lack of appropriate literature investigating the relation between the properties of biomass, the type of gasifier, and thermodynamic parameters of the gasification process, which justifies the scope of the present research to promote biomass as a renewable fuel for the future.

2.3. Power Production from Biomass

Regarding power production from biomass, most of the experimental facilities integrate an internal combustion engine (ICE) into the gasifier, coupled to a power generator. Accordingly, specific arrangements are necessary to make ICEs work with syngas, which has been a critical point as they usually operate with gasoline, diesel, and natural gas as fuels. Most of the engines available in the market are designed to operate with gasoline. Consequently, it is difficult to find a high efficiency engine that properly works with syngas. However, if the proper changes are made, an ICE can properly work with syngas; although, the obtained power is slightly lower [31]. There are examples in the technical bibliography of experimental adaptations of ICEs to be fed with syngas [32], such as the prototype designed by General Electric under the name “Jenbacher Gas Engine” [33]. Lastly, advanced numerical techniques have shown interesting results in dual-fuel engines powered with syngas; although, there is still an open issue related to the storage and transportation of the fuel that needs to be overcome [34].

3. Materials and Methods

3.1. Characterization of Biomass Waste: Pellet

For this experimental study, the biomass resource used was lignocellulosic pellets. The reason for choosing this kind of biomass waste was due to its chemical characteristics.

Lignocellulosic pellets are made up of different wood-like energy crops. Cellulose, hemicellulose, lignin, and extractives are found among the major components of this kind of biomass, as is shown in

Table 1. Pellets’ characterization.

Chemical Analysis
Ultimate analysis		Proximate analysis
Carbon (C)	47%	Fixed carbon	15%
Hydrogen (H)	7%	Volatile matter	76%
Oxygen (O)	45%	Ash	2%
Nitrogen (N)	2%	Moisture	6%
Sulfur (S)	0%	HHV (kJ/kg)	17.89
H/C	15%	LHV (kJ/kg)	16.22
O/C	96%	LHV/HHV	91%
Component Analysis
Cellulose (wt.% dry)	54.6
Lignin (wt.% dry)	16.2
Hemicellulose (wt.% dry)	27.0
Extractives (wt.% dry)	2.2

Source: Montuori et al. [20].

for dry fuel. This table also includes the proximate and ultimate analyses carried out according to the standard procedure (ASTM E1755–01).

Several pieces of equipment are necessary to handle the transportation, receipt, storage, and preparation of the biomass. For this experimental study, wood pieces were in situ transformed into pellets at the lab.

As shown in Figure 1, the pelletization process (transformation of wood pieces into pellets) consisted of three basic steps: grinding, milling, and pelletizing. First, once dried, wood pieces are transformed into chips by means of a process of hammer milling or grinding that produces woodchips of a large size. Then, by means of a disk mill, chips are reduced in size and converted into sawdust. Finally, by using a pellet machine, the sawdust is pressed and converted into pellets. As a result, cylindrical pellets with a diameter between 6 and 8 mm and a length from 10 to 30 mm were obtained.

3.2. Pilot Facility Description

The main characteristics of the designed pilot downdraft fixed-bed gasification power production facility (DGPP), implemented at the Polytechnic University of Valencia (UPV), are shown in

Table 2. DGGP characteristics.

Fuel	Pellets
Biomass diameter	0.5–5 cm
Biomass length	2–5 cm
Fuel consumption	5–10 kg/h (depending on size, moisture properties of the biomass, and the air/fuel relation)
Biomass deposit volume	0.23 m3
Storage capacity	40–90 kg (depending on biomass apparent density)
Autonomy	5–10 h
Motor–generator	PRAMAC Honda GX630 two-cylinder engine
Gas cooling medium	Water and wet scrubber.
Gas cleaning	Scrubber, tar separator pump, filter chips, filter fabric, and filter cotton
Water flow	1 m3/h

. The experimental facility consists of a reactor, a cooling and cleaning system, auxiliary and control systems, and an internal combustion engine coupled to an electric generator for power production. Moreover, to perform the experimental tests, the DGPP is equipped with an acquisition and measurement system by which the required variables are monitored. In addition, there is an automatic control system and a gas analyzer through which it is possible to determine the gas composition and the low heating value (LHV).

The experimental plant is equipped with a biomass deposit of 0.226 m³, equivalent to 45 kg of chips with a bulk density 200 kg/m³ which provides the gasifier with operational autonomy for approximately 4.5 h. Future studies will be focused on the implementation of a continuous feed system introducing biomass via the top of the reactor, using two valves with the installation of an intermediate tank to allow for the regulation of the biomass’s entrance into the reactor.

The aim of this analysis, based on data gathered in tests, is to reach a stable functioning of the DGPP while achieving the expected electrical power of 5 kW. The initial configuration of the experimental facility showed some flaws during its functioning, mainly due to the instable and high pressure drop recorded in the bed. Previous studies carried out by the authors [10,20] demonstrated that the amendments they implemented in the DGPP, listed below, succeeded in stabilizing the pressure drop to within the optimum range (<12.5 mbar):

• Increase in the diameter of the throat reactor from 7 cm to 10 cm (see Figure 2);
• Increase in the diameter of the grid from 220 mm up to 280 mm by adding an additional ring;
• Reduction in the height of the grid underneath the reducer cone by 1.5 cm (see Figure 2). The distance between the grid and the cone of the reactor influences the pressure drop in the bed, in this case reducing it. To vary this parameter, an auxiliary piece to support the grid was mounted;
• Installation of two automatic solenoid valves at the beginning of the air inlet pipe and the exhaust outlet pipe of the gasifier and at the beginning of the pipes of the torch and the motor.

This study aims to evaluate the effects of these performed amendments on maintaining the most critical operating parameters of the facility and validate the stable functioning of the 10 cm throat gasifier.

Previous studies [10,20] have demonstrated that these amendments succeeded in stabilizing the pressure drop to within the optimum range for the biomass power production facility’s proper functioning. Moreover, these modifications have the following effects:

• Reduces the total amount of biomass unburnt in the ashes deposit;
• Avoids the formation of holes;
• Reduces the ingress of unburnt air that could result in undesired combustion in the ash deposit.

Finally, the residues of biomass in the ash deposit are used as carbon fuel in the next test, so it is not considered as waste.

The methodology followed to implement the tests consisted of the following steps:

• Turning on the gasification facility;
• Operating the facility at different loads, increasing the load from 8 to 15 m³/h;
• For each load, measuring temperatures, pressures, flow rates, and electrical variables;
• According to the results obtained, the most significant operating parameters of the facility are determined:
  • Temperature at the reduction and combustion zones;
  • Air–fuel ratio;
  • Gas flow generated per kg of biomass consumed (m³/h·kg);
  • Percentage of intake air to total gas produced;
  • Gas velocity in the throat (fixed bed) (m/s);
  • Biomass processing capacity (kg/m²·h);
  • Electric power generated by the biomass;
  • Gas conversion efficiency;
  • Composition and calorific value of the produced gas;
• After each test, improvements to the gasification facility are considered and implemented;
• Repeating the same procedure to assess the effect on the operation of the gasification facility;
• Evaluating the results obtained through the comparison of the two configurations of the gasification facility.

Figure 3 shows the configuration of the biomass power production facility. Moreover, the scheme of the fixed-bed gasifier and the measurement points monitored during tests are shown in Figure 4.

Measured variables are as follows: gasifier inlet air flow (Q1_D); inlet air temperature of the gasifier (T1_D); temperatures of the pyrolysis zone (T2_D), combustion zone before the throat (T3_D), combustion and reduction zone (T4_D), reduction zone (T5_D), and ashes zone (T1_N); pressures of the biomass deposit (P1_D), the syngas bed (P2_D), the gas at the biomass deposit (P1_N), and the biomass bed (P2_N).

3.3. Instrumentation

The experimental plant is interfaced with a computer so that the data acquisition system provides a real-time reading of the temperature, pressure, and velocity of the inlet and outlet air flow. The metering system used for this research is composed of the following elements:

• Hot wire anemometers:

An EE65 Series anemometer is located at the reactor outlet pipe, providing the velocity and the temperature of the inlet air flow. Moreover, a CTV100 anemometer is located at the inlet pipe of the internal combustion engine, providing the velocity and the temperature of the inlet air pipe flow;

• Pressure transducers:

For the measurement of the pressure drops, a Series MS Magnesense Differential Pressure Transmitter has been used. The pressure transmitter is located at the outlet pipe of the reactor. The air/syngas mixture’s pressure at the engine inlet pipe is evaluated by a Series 616K Differential Pressure Transmitter, which is able to measure the air pressure at this point;

• K-type thermocouples:

The gasifier is equipped with a series of thermocouples, differential pressures gauges, and a control unit for the electrical parameters, which makes it possible to evaluate the whole gasifier temperature and pressure regimes;

• Gas analyzer:

Finally, the gas composition was determined by means of a gas model cubic analyzer, in particular, the portable Biogas Analyzer Gasboard 3200L. This analyzer, equipped with a proprietary infrared and electrochemical gas sensor, is able to measure the concentrations of CH₄, CO₂, H₂, H, CO, and O₂ using an NDIR sensor.

3.4. Experiments

To evaluate the experimental system performance, the following assumptions were made:

(1)

The system is in a steady state condition, the ambient conditions during all tests are the same, and the properties of all used biomass and air are uniform;

(2)

There is no pressure drop (defined as the difference between the atmospheric pressure and the pressure at the syngas bed);

(3)

The mass flow rate of the produced gas and air are approximately the same;

(4)

No occurrence of gas leakage. In order to verify this assumption, a preliminary test was conducted and, with no load, the produced gas volume flow rate measured was equal to the inlet air flow rate.

Each experiment was operated for about 2–2.5 h continuously, after the gasifier reached the steady state conditions. Experimental conditions are presented in

Table 3. Experiment conditions for tests 1 and 2.

	TEST 1 (150 min)			TEST 2 (117 min)
	Initial	Final	Difference	Initial	Final	Difference
Pellets (kg)	39.60	19.50	20.10	42.05	29.05	13.00
Char pellets (kg)	3.15	4.35	−1.20	2.40	3.60	−1.20
Total Biomass (kg)	42.75	23.85	18.90	44.45	32.65	11.80
	Average	Min	Max	Average	Min	Max
Air flow (Nm3/h)	11.17	8.00	16.07	10.50	8.00	15.06
Biomass consumption (kg/h)	7.56			6.05
Air/Biomass (Nm3/kg)	1.48			1.74
Air intro/Stoich. Rate (%)	31.80			37.3

. Finally, the residues of biomass in the ash deposit were used as carbon fuel in the next test, so it was not considered as waste.

The reliability of the new configuration of the pilot model design has been assessed by means of the thermodynamic parameters discussed in the following section, calculated using the key measurement points of the DGPP.

4. Definition of the Theoretical Process Parameters

4.1. Lower Heating Value (LHV)

LHV is calculated experimentally according to Equation (1) where ${LHV}_{CO}$, ${LHV}_{H_2},$ and ${LHV}_{C{H}_4}$ are equal to 10,110 kJ/kg, 119,494 kJ/kg, and 49,915 kJ/kg, respectively [35,36]. [%CO, %CH₄] and [%H₂] are the mole fractions of the syngas components and were determined by means of the portable gas analyzer.

$$LH{V}_{gas}=[\%CO]\cdot LH{V}_{CO}+[\%C{H}_4]\cdot LH{V}_{C{H}_4}+[\%H_2]\cdot LH{V}_{H_2}$$

(1)

4.2. Gasifier Efficiency (η_con) and Motor–Generator Efficiency (η_mot-gen)

The global performance of the transformation from biomass to electrical power through syngas includes two partial transformations: firstly, the conversion of biomass to syngas, taking place in the gasifier (η_con). Secondly, the production of electricity from the syngas by means of an adapted internal combustion motor (ICM) directly fed by syngas and coupled to an electric generator (η_mot-gen). η_con is calculated as the ratio of the syngas energy outlet rate and the biomass energy inlet rate, as shown in Equation (2), where ${\dot{V}}_{syngas}$ and ${\dot{m}}_{biomass}$ are the volume and mass flow rates of syngas and biomass, respectively.

$${\eta }_{con}={\displaystyle \frac{E_{syngas}}{E_{biomass}}}={\displaystyle \frac{{\dot{V}}_{syngas}\cdot LH{V}_{syngas}}{{\dot{m}}_{biomass}\cdot LH{V}_{biomass}}}$$

(2)

With E_out being the electric power produced from the syngas combustion, the performance of the block motor–generator (η_mot-gen) is calculated by means of Equation (3):

$${\eta }_{mot\text{-}gen}={\displaystyle \frac{E_{out}}{{\dot{V}}_{syngas}\cdot LH{V}_{syngas}}}$$

(3)

Power generation (E_out) is directly related to the quality of syngas, its LHV, composition, and impurities (like tar). A block ICM-generator has been proven to be economically feasible for capacities from 5 kWe and above [37], so its use is justified in this case. This power has been measured by means of a network analyzer.

4.3. Combustion and Reduction Temperature

Temperatures of the processes to obtain syngas from biomass have an impact on the composition of the produced syngas because there is a direct relation between temperature, components’ concentration, and the conversion efficiency. During experiments, measurements of temperatures in the reduction and combustion zones of the gasifier were recorded (Figure 4), demonstrating that these two parameters are directly correlated. Conversely, the combustion and the reduction temperatures were analyzed as a function of the inlet air flow.

Previous studies [38,39] demonstrated that, for the proper gasification of lignocellulosic biomass in a downdraft gasifier, the combustion and reduction temperatures should be in the range of 800–1000 °C and 500–700 °C, respectively (see Figure 5). During tests, these values were validated.

5. Discussion and Results

5.1. Electrical Power and Syngas Production

During Test 1, the air flow changed from 8 to 16 Nm³/h. The gasifier was turned on and, after 50 min, the engine (ICM-generator block) was also turned on. There was no observed increase in water in the filter, and the pressure drop was steady. Therefore, amendments implemented in the gasification facility, described in Section 3.2, provided positive results, with pressure drop increments in the range of pressures established by the literature, between 8 and 12 mbar (Figure 6 left).

Thus, the volume of syngas produced, which depends on the inlet air flow, also increases. As a result, the DGPP reached a maximum electrical power of 5 kW in steady-state conditions, as shown in Figure 6 (right) from minute 92 to minute 99, when the engine was switched on. Similarly, the gasifier was fueled with 42.05 kg of sieved pellets mixed with 2.40 kg of coal char pellets during Test 2. At the end of the test, the total biomass consumption was 11.8 kg, while the air flow varied from 8 to 15 Nm³/h. The water level in the filter was stable, as well as the pressure drop, and the electrical power was stable at approximately 4.8–5 kW. Test 2 (Figure 7) proved that the operation of the experimental plan was feasible, similar to Test 1, again validating the ability of the gasifier design to meet an electric power of 5 kW in correspondence to the maximum syngas production. Indeed, the pressure drop shows minimal oscillations, being bounded within appropriate values for stable operation of the gasification facility.

5.2. LHV of Syngas, Global Efficiency, and Temperatures Inside the Gasifier

According to Figure 8 (left), the variation in the inlet air flow rate in Test 2, from 8.5 to 11.5 Nm³/h, produced a variation in the LHV of the syngas from 5.3 to 6.5 MJ/Nm³. Similarly, in Test 1, a variation in the inlet air flow between 9.64 Nm³/h and 13.87 Nm³/h produced a lower heat value varying between 5.3 and 6.5 MJ/Nm³. Consequently, for a variation in flow between 8.50 and 11 Nm³/h, the LHV of syngas ranged between 5.3 and 6.57 MJ/Nm³, giving an average value of 5.95 MJ/Nm³, which is in the order of magnitude of the result obtained by other researchers in similar applications [40].

Considering the obtained values, the efficiency of conversion of the gasifier, evaluated by Equation (2), is equal to 79.8%. This is a high cold gas efficiency but within the usual range between 75% and 90%, as studied by Thompson et al. [41]. Applying Equation (3), the ICM-generator efficiency was 22% while the power production facility was working in a steady state and producing a maximum power of 5 kW. Therefore, the global efficiency of the DGPP is 17.6%. Additionally, the profiles of the reduction and combustion temperatures obtained experimentally are represented in Figure 8 (right). As shown, once a steady state is reached, after 10–15 min, the reduction temperature bounces between 600 and 700 °C, while the combustion temperature varies between 800 and 900 °C. Therefore, as stated in Section 4.3, the obtained values are within the ranges studied in the bibliography for this kind of gasifier.

6. Conclusions

This paper provides an experimental study of the behavior of a pilot downdraft fixed-bed gasification facility for power production, with the aim of contributing to the diffusion of biomass technology on a small-scale basis. Experiments presented in this paper were performed after implementing technical modifications to the throat design, the air inlet system, and the biomass deposit of the pilot facility. By means of the improvement to the gasifier design, a stable functioning of the gasification facility was achieved with a reduction in pressure fluctuations, reaching the target power of 5 kWe. Thus, the bed pressure drop was maintained within the recommended range of values (between 8 and 12.5 mbar) established by previous scientific studies. Additionally, the relation between the LHV of the produced syngas and the air flow inlet was determined, being the first variable directly related to the second one with values between 5.3 and 6.6 MJ/Nm³. The global performance of the facility was evaluated to be 17.6%, whereas the conversion efficiency corresponding to the gasifier was 79.8%. Furthermore, the combustion and reduction temperatures were analyzed, showing that these results were obtained under the proper operation of the experimental power production facility.

The presented research uses a two-cylinder engine, opening the gate to future research focused on the study of the use of a four-cylinder engine for power generation fueled by biomass, where additional benefits could be expected for several reasons. Firstly, the fluctuations in the air–syngas ratio are expected to decrease significantly for a four-cylinder engine due to the lower speed. Secondly, the volumetric efficiency of a four-cylinder engine is greater and, consequently, the losses are lower. Furthermore, the time for gasification reactions increases, resulting in a lower production of unburnt components and, therefore, a better efficiency of the whole gasification facility. On the other side, the growing social awareness about the unhealthful impact of fossil fuels in ICEs, as well as mobility, will bring new research interests related to the utilization of syngas in this kind of engine. Accordingly, the variety of possible ICE configurations requires further experimental studies to achieve full comprehension of the design parameters for engines fed with syngas. Finally, the design and implementation of a biomass resource market should be further explored in order to expand the utilization of this renewable fuel and facilitate the availability of this resource in time and according to the demand.