# Effects of Propanol on the Performance and Emissions of a Dual-Fuel Industrial Diesel Engine
## 1 Introduction  
Compression ignition internal combustion engines are used in transport and heavy construction machinery and are a source of propulsion for generators due to their high durability, high power, and relatively low fuel consumption [1]. These engines combust mixtures with a large excess of air (lean mixtures) and thus they have lower emissions of CO and THC compared to spark ignition engines [2]. A significant limitation of these engines is their soot emission [3]. For this reason, alternative combustion systems and alternative fuels are used. Another two important factors prompting the use of alternative fuels are the constantly growing oil prices and the instability of the fuel market. The diversification of fuel sources is very important for industries to ensure energy stability [4]. Biofuels [5] are an alternative fuel to fossil fuels, and alcohols are a large group of biofuels. They are renewable fuels because they can be produced from biomass [6]. Additionally, alcohol-based fuels contain oxygen in their molecular structure, and thus can reduce the emission of some exhaust components, such as soot [7]. Alcohol-based fuels cannot be a substitute for diesel or biodiesel due to their self-ignition limitations. They are characterized by a low value of the cetane number, which adversely affects the self-ignition of these fuels, and which during combustion may result in knock combustion. Another disadvantage is the poor lubricating properties of alcohols, which contribute to faster wear of the engine injection elements [8]. Another disadvantage of alcohols is their lower calorific value in relationto diesel, which requires larger doses supplied to the engine to ensure sufficiently high engine power [9]. Piston engines are powered by both lower alcohols, such as methanol and ethanol, and higher alcohols, such as butanol or propanol [10]. Higher alcohols have properties similar to diesel fuel. This applies to both their relatively high calorific value and their cetane number or density [6]. Moreover, alcohols are characterized by a higher value of the heat of vaporization compared to diesel fuel. One of the interesting alcoholic fuels is propanol, which has better properties than methanol or ethanol. Currently, alcohols are viewed as an oxygen enriched additive that can be co-combusted with diesel fuel/biodiesel to intensify the combustion process in a compression ignition engine. Alcohols can be used as an additive to diesel fuel, but there are difficulties with the miscibility of both fuels whereby phase separation can occur [11]. To create a stable mixture, various types of stabilizers, such as n-pentanol and tetrahydrofuran, are used [12,13]. As shown by the results of extensive research, the alcohol content in the mixture with diesel fuel is limited to about 20% by volume [14]. Alcohols mix better with biodiesel and are closer to each other in terms of their molecular structure [15]. The technology devoid of these drawbacks is the dual-fuel engine, where the co-combusted fuels are delivered separately. Alcoholic fuel is fed to the intake manifold during the cylinder intake stroke (PFI--Port Fuel Injection), and diesel or biodiesel is fed directly to the combustion chamber to initiate combustion [16]. A dual fuel system is one of the most effective techniques for using alternative fuels to power the industrial engine. This technology allows for almost any share of fuels supplying the engine depending on its load or resources [17]. The share of alcohol in the combustion process significantly affects both the course of the combustion process, its phases, and the emission of exhaust gases. The alcohol that is fuel injected into the intake manifold, due to the high value of the heat of vaporization, causes the decrease in the temperature of fresh charge before the combustion is initiated with a dose of diesel fuel. This contributes to an increase in ignition delay along with an increase in the share of alcohol fuel [18].